LegendreP[n, x] gives the Legendre polynomial P_n (x). LegendreP[n, m, x] gives the associated Legendre polynomial P_n^m(x).
LerchPhi[z, s, a] gives the Lerch transcendent \[CapitalPhi] (z, s, a).
LinearModelFit[{y_1, y_2, ...}, {f_1, f_2, ...}, x] constructs a linear model of the form \[Beta]_0 + \[Beta]_1 f_1 + \[Beta]_2 f_2 + ... that fits the y_i for successive x ...
LogGamma[z] gives the logarithm of the gamma function log \[CapitalGamma](z).
LucasL
(Built-in Mathematica Symbol) LucasL[n] gives the Lucas number L_n.LucasL[n, x] gives the Lucas polynomial L_n (x).
Multinomial[n_1, n_2, ...] gives the multinomial coefficient (n_1 + n_2 + ...)!/(n_1! n_2! ...).
NevilleThetaD[z, m] gives the Neville theta function \[CurlyTheta]_d (z \[VerticalSeparator] m).
NevilleThetaN[z, m] gives the Neville theta function \[CurlyTheta]_n (z \[VerticalSeparator] m).
NevilleThetaS[z, m] gives the Neville theta function \[CurlyTheta]_s (z \[VerticalSeparator] m).
NonlinearModelFit[{y_1, y_2, ...}, form, {\[Beta]_1, ...}, x] constructs a nonlinear model with structure form that fits the y_i for successive x values 1, 2, ... using the ...