cp's OEIS Frontend

A064461 First row of Pascal's triangle that has n distinct nonsquarefree entries, or -1 if no such row exists.

%I A064461 #18 Jan 18 2018 08:24:48
%S A064461 0,4,13,8,9,12,17,20,16,18,26,24,62,27,34,33,32,-1,36,40,-1,95,-1,79,
%T A064461 48,50,54,60,56,74,67,65,64,73,-1,94,72,91,85,83,80,84,119,88,-1,97,
%U A064461 104,101,96,98,100,-1,115,-1,108,114,112,123,122,120,121,125,131
%N A064461 First row of Pascal's triangle that has n distinct nonsquarefree entries, or -1 if no such row exists.
%C A064461 Numbers such that a(n) is -1: 17, 20, 22, 34, 44, 51, ... - _Michel Marcus_, Mar 05 2014
%e A064461 a(2) = 13 because C(13,5) = 3^2*11*13 and C(13,6) = 2^2*3*11*13.
%t A064461 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} ]
%o A064461 (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
%Y A064461 Cf. A064460, A064462, A048276.
%K A064461 sign
%O A064461 0,2
%A A064461 _Robert G. Wilson v_, Oct 02 2001
%E A064461 Corrected and extended by _Michel Marcus_, Mar 05 2014