

A171611


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


4



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
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OFFSET

1,9


LINKS

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


EXAMPLE

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


MAPLE

A171611 := proc(n) a := 0 ; for i from 3 do p := ithprime(i) ; q := 2*np ; 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 *)


CROSSREFS

Cf. A045917, A169546.
Sequence in context: A319178 A254041 A240712 * A239507 A216448 A216763
Adjacent sequences: A171608 A171609 A171610 * A171612 A171613 A171614


KEYWORD

nonn


AUTHOR

JuriStepan Gerasimov, Dec 13 2009


EXTENSIONS

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


STATUS

approved



