OFFSET
0,2
COMMENTS
Numbers such that a(n) is -1: 17, 20, 22, 34, 44, 51, ... - Michel Marcus, Mar 05 2014
EXAMPLE
a(2) = 13 because C(13,5) = 3^2*11*13 and C(13,6) = 2^2*3*11*13.
MATHEMATICA
f[ n_ ] := (c = 0; k = 1; While[ k < n/2 + .5, If[ Union[ Transpose[ FactorInteger[ Binomial[ n, k ] ] ] [ [ 2 ] ] ] [ [ -1 ] ] > 1, c++ ]; k++ ]; c); Do[ m = 2; While[ f[ m ] != n, m++ ]; Print[ m ], {n, 0, 16} ]
PROG
(PARI) a(n, v) = {for (i=1, #v, if (v[i] == n, return (i-1)); ); return (-1); } \\ where v is vector A064460; Michel Marcus, Mar 05 2014
CROSSREFS
KEYWORD
sign
AUTHOR
Robert G. Wilson v, Oct 02 2001
EXTENSIONS
Corrected and extended by Michel Marcus, Mar 05 2014
STATUS
approved