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

Author

Asher Auel, May 20 2001

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Cf. A000217, A061304.

Programs

PARI

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