A160973 a(n) is the number of positive integers of the form (n-3k)/(2k+1), 1 <= k <= (n-1)/5.

0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 2, 0, 1, 0, 0, 3, 0, 1, 1, 0, 2, 1, 0, 0, 3, 2, 0, 1, 0, 0, 3, 2, 0, 2, 0, 2, 1, 0, 2, 1, 2, 0, 3, 0, 0, 5, 0, 0, 1, 0, 2, 3, 2, 1, 1, 2, 0, 1, 0, 2, 5, 0, 0, 1, 2, 2, 3, 0, 0, 3, 2, 0, 1, 2, 0, 5, 0, 1, 3, 0, 4, 1, 0, 0, 1

Offset

0,17

Comments

If n is different from 3, then a(n)=0 iff n is in A067076, i.e., 2n+3 is prime.

Links

Table of n, a(n) for n=0..90.

Mathematica

a[n_] := Length[Select[Range[Floor[(n-1)/5]], IntegerQ[(n-3#)/(2#+1)] &]]; Array[a, 100, 0] (* Amiram Eldar, Dec 15 2018 *)

Prog

(PARI) a(n) = sum(k=1, (n-1)/5, frac((n-3*k)/(2*k+1)) == 0); \\ Michel Marcus, Dec 15 2018

Crossrefs

Cf. A067076, A034953, A054269, A082749, A006254, A161116.

Sequence in context: A355607 A253184 A242086 * A036853 A036852 A260941

Adjacent sequences: A160970 A160971 A160972 * A160974 A160975 A160976

Keyword

nonn

Author

Vladimir Shevelev, Jun 01 2009, Jun 07 2009

Extensions

Edited by N. J. A. Sloane, Jun 07 2009

a(44) corrected and more terms from Michel Marcus, Dec 15 2018

Status

approved