A152671 Even Catalan numbers divided by 2.

1, 7, 21, 66, 715, 2431, 8398, 29393, 104006, 371450, 1337220, 17678835, 64822395, 238819350, 883631595, 3282060210, 12233133510, 45741281820, 171529806825, 644952073662, 2430973200726, 9183676536076, 34766775458002

Offset: 1

Author

Omar E. Pol, Dec 10 2008

Keywords

• easy
• nonn

Crossrefs

Cf. A000108, A152670.

Programs

Mathematica

Select[CatalanNumber[Range[30]], EvenQ]/2 (* Vladimir Reshetnikov, Nov 02 2015 *)

PARI

lista(nn) = for (n=1, nn, if (((c=binomial(2*n,n)/(n+1)) % 2) == 0, print1(c/2, ", "))); \\ Michel Marcus, Nov 02 2015

Formula

a(n) = A152670(n)/2.