A061900 Triangular numbers that are not squarefree.

28, 36, 45, 120, 136, 153, 171, 276, 300, 325, 351, 378, 496, 528, 630, 666, 780, 820, 990, 1035, 1128, 1176, 1225, 1275, 1431, 1485, 1540, 1596, 1953, 2016, 2080, 2556, 2628, 2775, 2850, 3160, 3240, 3321, 3828, 3916, 4005, 4095, 4560, 4656, 4753, 4851

Offset

1,1

Links

Harry J. Smith, Table of n, a(n) for n = 1..1000

Example

36 and 45 are triangular numbers (A000217) and are not squarefree: 36 = (2^2)(3^2), 45 = (3^2)(5).

Mathematica

Select[Accumulate[Range[100]], !SquareFreeQ[#]&] (* Harvey P. Dale, Jan 03 2026 *)

Prog

(PARI) { n=t=0; for (i=1, 1926, t+=i; if (!issquarefree(t), write("b061900.txt", n++, " ", t)) ) } \\ Harry J. Smith, Jul 28 2009

Crossrefs

Cf. A000217, A061304.

Sequence in context: A167308 A303261 A168106 * A048023 A359529 A105710

Adjacent sequences: A061897 A061898 A061899 * A061901 A061902 A061903

Keyword

nonn

Author

Asher Auel, May 20 2001

Status

approved