A119356 Square pyramidal number (A000330) n(n+1)(2n+1)/6 is squarefree.

1, 2, 3, 4, 5, 6, 9, 10, 11, 14, 17, 18, 19, 20, 21, 22, 28, 29, 30, 33, 34, 35, 36, 38, 41, 42, 43, 44, 45, 46, 51, 52, 57, 58, 59, 61, 65, 66, 68, 69, 70, 76, 77, 78, 82, 83, 85, 86, 89, 90, 91, 92, 93, 101, 102, 105, 106, 109, 110, 113, 114, 115, 116, 117, 118, 123, 126

Offset

1,2

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

10 is OK because 10*11*(2*10+1)/6 = 5*7*11 is squarefree.

Maple

filter:= n -> numtheory:-issqrfree(n*(n+1)*(2*n+1)/6):
select(filter, [$1..200]); # Robert Israel, Aug 04 2020

Prog

(PARI) lista(nn) = {for (n=1, nn, if (issquarefree(n*(n+1)*(2*n+1)/6), print1(n, ", ")); ); } \\ Michel Marcus, May 18 2013

Crossrefs

Cf. A000330, A005117.

Sequence in context: A168009 A134697 A032975 * A137582 A116965 A356007

Adjacent sequences: A119353 A119354 A119355 * A119357 A119358 A119359

Keyword

nonn

Author

Zak Seidov, May 16 2006

Status

approved