OFFSET
1,7
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..500
FORMULA
a(n) = [x^4] Product_{k=4..n+2} (x^prime(k) + 1/x^prime(k)). - Ilya Gutkovskiy, Jan 28 2024
EXAMPLE
a(7) counts these 3 solutions: {5, -7, 11, 13, -17, 19, -23}, {5, 7, -11, -13, 17, 19, -23}, {5, 7, -11, 13, -17, -19, 23}.
MATHEMATICA
{f, s} = {3, 1}; Table[t = Map[Prime[# + f - 1] &, Range[2, z]]; Count[Map[Apply[Plus, #] &, Map[t # &, Tuples[{-1, 1}, Length[t]]]], s - Prime[f]], {z, 22}]
(* A022901, a(n) = number of solutions of "sum = s" using Prime(f) to Prime(f+n-1) *)
n = 7; t = Map[Prime[# + f - 1] &, Range[n]]; Map[#[[2]] &, Select[Map[{Apply[Plus, #], #} &, Map[t # &, Map[Prepend[#, 1] &, Tuples[{-1, 1}, Length[t] - 1]]]], #[[1]] == s &]] (* the 3 solutions of using n=7 primes; Peter J. C. Moses, Oct 01 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Corrected and extended by Clark Kimberling, Oct 01 2013
a(23)-a(50) from Alois P. Heinz, Aug 06 2015
STATUS
approved