A171611 From Goldbach problem: number of decompositions of 2n into unordered sums of two primes > 3.

0, 0, 0, 0, 1, 1, 1, 1, 2, 1, 2, 3, 2, 2, 3, 1, 3, 4, 2, 2, 4, 2, 3, 5, 3, 3, 5, 2, 4, 6, 2, 4, 6, 2, 4, 6, 4, 4, 7, 4, 4, 8, 4, 4, 9, 3, 5, 7, 3, 5, 8, 4, 5, 8, 5, 6, 10, 5, 6, 12, 4, 5, 10, 3, 6, 9, 5, 5, 8, 6, 7, 11, 6, 5, 12, 3, 7, 11, 5, 7, 10, 5, 5, 13, 8, 6, 11, 6, 7, 14, 5, 7, 13, 5, 8, 11, 6, 8, 13

Offset: 1

Author

Juri-Stepan Gerasimov, Dec 13 2009

Keywords

• nonn

Examples

			a(5)=1 because 2*5 = 5 + 5.
		

Links

• Lei Zhou, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A045917, A169546.

Programs

Maple

A171611 := proc(n) a := 0 ; for i from 3 do p := ithprime(i) ; q := 2*n-p ; if q < p then return a ; end if; if isprime(q) then a := a+1 ; end if; if q <= p then return a ; end if; end do: end proc:
seq(A171611(n), n=1..120) ; # R. J. Mathar, May 22 2010

Mathematica

Table[s = 2*n; ct = 0; p = 3; While[p = NextPrime[p]; p <= n, If[PrimeQ[s - p], ct++]]; ct, {n, 100}] (* Lei Zhou, Apr 10 2014 *)

Extensions

a(38) changed from 5 to 4 and a(79) and a(82) changed by R. J. Mathar, May 22 2010