OFFSET
0,10
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..20000 (first 1001 terms from Joseph Myers)
British Mathematical Olympiad 2015/16, Olympiad Round 1, Problem 6, Friday, 27 November 2015.
FORMULA
G.f.: (1+x)(1+x^3)(1+x^5)(1+x^9)(1+x^15)....
EXAMPLE
28 = 27 + 1 = 25 + 3 = 15 + 9 + 3 + 1, so a(28) = 3.
MATHEMATICA
nmax = 100; A003593 = Select[Range[nmax], PowerMod[15, #, #] == 0 &]; CoefficientList[Series[Product[(1 + x^(A003593[[k]])), {k, 1, Length[A003593]}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Dec 01 2015 *)
PROG
(Haskell)
import Data.MemoCombinators (memo2, list, integral)
a264997 n = a264997_list !! (n-1)
a264997_list = f 0 [] a003593_list where
f u vs ws'@(w:ws) | u < w = (p' vs u) : f (u + 1) vs ws'
| otherwise = f u (vs ++ [w]) ws
p' = memo2 (list integral) integral p
p _ 0 = 1
p [] _ = 0
p (k:ks) m = if m < k then 0 else p' ks (m - k) + p' ks m
-- Reinhard Zumkeller, Dec 18 2015
CROSSREFS
KEYWORD
AUTHOR
Joseph Myers, Nov 29 2015
STATUS
approved