A258713 A001172(n)/2: Least k such that 2k is a sum of two odd primes in exactly n ways.

0, 3, 5, 11, 17, 24, 30, 39, 42, 45, 57, 72, 60, 84, 90, 117, 123, 144, 120, 105, 162, 150, 180, 237, 165, 264, 288, 195, 231, 240, 210, 285, 255, 336, 396, 378, 438, 357, 399, 345, 519, 315, 504, 465, 390, 480, 435, 462, 450, 567, 717, 420, 495, 651

Offset

0,2

Comments

Up to a(14) also indices of records in A002375, number of ways to write 2n as sum of two odd primes. - M. F. Hasler, Aug 21 2017

Links

Robert Israel, Table of n, a(n) for n = 0..845

Maple

g:= add(x^ithprime(i), i=2..1000):
G:= series((g^2+add(x^(2*ithprime(i)), i=2..1000))/2, x, ithprime(1001)+3):
A[0]:= 0:
for k from 1 to (ithprime(1001)+1)/2 do
  m:= coeff(G, x, 2*k);
  if not assigned(A[m]) then A[m]:= k fi;
od:
for m from 1 while assigned(A[m]) do od:
seq(A[i], i=0..m-1); # Robert Israel, Aug 21 2017

Mathematica

With[{s = Array[Count[Select[IntegerPartitions[2 #, 2], Length@ # == 2 &], p_ /; AllTrue[p, And[PrimeQ@ #, OddQ@ #] &]] &, 10^3]}, Table[FirstPosition[s, n][[1]] /. 1 -> 0, {n, 0, 53}]] (* Michael De Vlieger, Aug 21 2017 *)

Crossrefs

Cf. A136244, A001172.

Cf. A002375, A002372, A045917.

Sequence in context: A099596 A200748 A063693 * A267517 A309427 A211435

Adjacent sequences: A258710 A258711 A258712 * A258714 A258715 A258716

Keyword

nonn

Author

N. J. A. Sloane, Jun 14 2015

Extensions

Edited by M. F. Hasler, Aug 21 2017

Edited by Robert Israel, Aug 21 2017

Status

approved