OFFSET
1,1
COMMENTS
Is 2213 the largest prime term that can be expressed as the sum of two proper prime powers in more than one way? - Altug Alkan, Jul 22 2017
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
Exponents in expansion of (Sum_{k>=1} x^A246547(k))^2.
EXAMPLE
13 is in the sequence because 13 = 2^2 + 3^2.
MAPLE
N:= 1000: # to get all terms <= N
P:= select(isprime, [$2..floor(sqrt(N))]):
PP:= {seq(seq(p^j, j=2..floor(log[p](N))), p=P)}:
A:= select(`<=`, {seq(seq(PP[i]+PP[j], j=1..i), i=1..nops(PP))}, N):
sort(convert(A, list)); # Robert Israel, Jul 21 2017
MATHEMATICA
nmax = 180; f[x_] := Sum[Boole[PrimePowerQ[k] && PrimeOmega[k] > 1] x^k, {k, 1, nmax}]^2; Exponent[#, x] & /@ List @@ Normal[Series[f[x], {x, 0, nmax}]]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jul 20 2017
STATUS
approved