Other functions with an optional non-last argument (including Eike's index). I included functions where the last two arguments were optional, reasoning that the next to last argument could be omitted, yet the last argument be present.
6.10.14 NETWORKDAYS
Summary: Returns the whole number of work days between two dates.
Syntax: NETWORKDAYS( DateParam Date1 ; DateParam Date2 [ ; [ DateSequence holidays ] [ ;
LogicalSequence workdays ] ] )
6.10.22 WORKDAY
Summary: Returns the date serial number which is a specified number of work days before or
after an input date.
Syntax: WORKDAY( DateParam Date ; Number Offset [ ; [ DateSequence Holidays ] [ ;
LogicalSequence Workdays ] ] )
6.12.2 ACCRINT
Summary: Calculates the accrued interest for securities with periodic interest payments.
Syntax: ACCRINT( DateParam issue ; DateParam first ; DateParam settlement ; Number
coupon ; Number par ; Integer frequency [ ; Basis basis = 0 [ ; Logical calc_method = TRUE() ] ] )
6.12.20 FV
Summary: Compute the future value (FV) of an investment.
Syntax: FV( Number Rate ; Number Nper ; Number Payment [ ; [ Number Pv = 0 ] [ ; Number
PayType = 0 ] ] )
6.12.23 IPMT
Summary: Returns the amount of an annuity payment going towards interest.
Syntax: IPMT( Number Rate ; Number Period ; Number Nper ; Number PV [ ; Number FV = 0 [ ;
Number Type = 0 ] ] )
6.12.29 NPER
Summary: Compute the number of payment periods for an investment.
Syntax: NPER( Number Rate ; Number Payment ; Number Pv [ ; [ Number Fv ] [ ; Number
PayType ] ] )
6.12.36 PMT
Summary: Compute the payment made each period for an investment.
Syntax: PMT( Number Rate ; Integer Nper ; Number Pv [ ; [ Number Fv = 0 ] [ ; Number PayType
= 0 ] ] )
6.12.37 PPMT
Summary: Calculate the payment for a given period on the principal for an investment at a given
interest rate and constant payments.
Syntax: PPMT( Number Rate ; Integer Period ; Integer nPer ; Number Present [ ; Number Future
= 0 [ ; Number Type = 0 ] ] )
6.12.41 PV
Summary: Compute the present value (PV) of an investment.
Syntax: PV( Number Rate ; Number Nper ; Number Payment [ ; [ Number Fv = 0 ] [ ; Number
PayType = 0 ] ] )
6.12.42 RATE
Summary: Compute the interest rate per period of an investment.
Syntax: RATE( Number Nper ; Number Payment ; Number Pv [ ; [ Number Fv = 0 ] [ ; [ Number
PayType = 0 ] [ ; Number Guess = 0.1 ] ] ] )
6.12.50 VDB
Summary: Calculates the depreciation allowance of an asset with an initial value, an expected
useful life, and a final value of salvage for a period specified, using the variable-rate declining
balance method..
Syntax: VDB( Number cost ; Number salvage ; Number lifeTime ; Number startPeriod ; Number
endPeriod [ ; Number depreciationFactor = 2 [ ; Logical noSwitch = FALSE() ] ] )
6.13.28 NUMBERVALUE
Summary: Convert text to number, in a locale-independent way
Syntax: NUMBERVALUE( Text X [ ; Text DecimalSeparator [ ; Text GroupSeparator ] ] )
6.14.2 ADDRESS
Summary: Returns a cell address (reference) as text
Syntax: ADDRESS( Integer Row ; Integer Column [ ; Integer Abs = 1 [ ; Logical A1 = TRUE() [ ;
Text Sheet ] ] ] )
6.14.6 INDEX
Summary: Returns a value using a row and column index value (and optionally an area index).
Syntax: INDEX( ReferenceList|Array DataSource ; [ Integer Row ] [ ; [ Integer Column ] ] [ ;
Integer AreaNumber = 1 ] )
6.14.11 OFFSET
Summary: Modifies a reference's position and dimension.
Syntax: OFFSET( Reference reference ; Integer rowOffset ; Integer columnOffset [ ; [ Integer
newHeight ] [ ; [ Integer newWidth ] ] ] )
6.15.4 IF
Summary: Return one of two values, depending on a condition
Syntax: IF( Logical Condition [ ; [ Any IfTrue ] [ ; [ Any IfFalse ] ] ] )
6.16.29 EUROCONVERT
Summary: Converts a Number, representing a value in one European currency, to an equivalent
value in another European currency, according to the fixed conversion rates defined by the
Council of the European Union.
Syntax: EUROCONVERT( Number N ; Text From ; Text To [ ; Logical FullPrecision = FALSE() [ ;
Integer TriangulationPrecision ] ] )
6.17.1 CEILING
Summary: Round a number N up to the nearest multiple of the second parameter, significance.
Syntax: CEILING( Number N [ ; [ Number significance ] [ ; Number mode ] ] )
6.17.3 FLOOR
Summary: Round a number N down to the nearest multiple of the second parameter,
significance.
Syntax: FLOOR( Number N [ ; [ Number significance ] [ ; Number mode ] ] )
6.18.7 BETADIST
Summary: returns the value of the probability density function or the cumulative distribution
function for the beta distribution.
Syntax: BETADIST( Number x ; Number a ; Number b [ ; Number a = 0 [ ; Number b = 1 [ ;
Logical Cumulative = TRUE() ] ] ] )
6.18.8 BETAINV
Summary: returns the inverse of BETADIST(x;a;b;a;b;TRUE()).
Syntax: BETAINV( Number p ; Number a ; Number b [ ; Number a = 0 [ ; Number b = 1 ] ] )
6.18.35 GROWTH
Summary: Returns predicted values based on an exponential regression.
Syntax: GROWTH( Array knownY [ ; [ Array knownX ] [ ; [ Array newX ] [ ; Logical Const =
TRUE() ] ] ] )
6.18.41 LINEST
Summary: Returns the parameters of the (simple or multiple) linear regression equation for the
given data and, optionally, statistics on this regression.
Syntax: LINEST( Array knownY [ ; [ Array knownX ] [ ; Logical Const = TRUE() [ ; Logical Stats =
FALSE() ] ] ] )
6.18.42 LOGEST
Summary: Returns the parameters of an exponential regression equation for the given data
obtained by linearizing this intrinsically linear response function and returns, optionally, statistics
on this regression.
Syntax: LOGEST( Array knownY [ ; [ Array knownX ] [ ; Logical Const = TRUE() [ ; Logical Stats =
FALSE() ] ] ] )
6.18.43 LOGINV
Summary: returns the inverse of LOGNORMDIST(x;Mean;StandardDeviation,TRUE()).
Syntax: LOGINV( Number p [ ; Number Mean = 0 [ ; Number StandardDeviation = 1 ] ] )
6.18.44 LOGNORMDIST
Summary: returns the value of the probability density function or the cumulative distribution
function for the lognormal distribution with the mean and standard deviation given.
Syntax: LOGNORMDIST( Number x [ ; Number m = 0 [ ; Number s = 1 [ ; Logical Cumulative =
TRUE() ] ] ] )
6.18.79 TREND
Summary: Returns predicted values based on a simple or multiple linear regression.
Syntax: TREND( Array knownY [ ; [ Array knownX ] [ ; [ Array newX ] [ ; Logical Const =
TRUE() ] ] ] )
6.20.10 FIXED
Summary: Round the number to a specified number of decimals and format the result as a text.
Syntax: FIXED( Number N [ ; Integer D = 2 [ ; Logical OmitSeparators = FALSE() ] ] )
Eike says INDEX is an existing function with optional non-last arguments
http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part2.html#INDEX