A074315 Abundant triangular numbers.

36, 66, 78, 120, 210, 276, 300, 378, 528, 630, 666, 780, 820, 990, 1128, 1176, 1326, 1540, 1596, 1770, 1830, 2016, 2080, 2346, 2556, 2628, 2850, 3160, 3240, 3486, 3570, 3828, 4095, 4278, 4560, 4656, 4950, 5460, 5778, 5886, 6216, 6328, 6786, 7140, 7260

Offset: 1

Author

Shyam Sunder Gupta, Sep 22 2002

Keywords

• nonn

Examples

			a(2) = 66 because the sum of aliquot divisors of 66 (which is a triangular number) is 1+2+3+6+11+22+33 = 78 which is greater than 66, hence it is abundant. 66 is the 2nd abundant triangular number.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harvey P. Dale)

Crossrefs

Cf. A000217, A005101.

Programs

Mathematica

Select[Accumulate[Range[150]],Total[Divisors[#]]>2#&] (* Harvey P. Dale, Dec 18 2014 *)

PARI

listA074315(m) = {for (i=1, m, t = i*(i+1)/2; if (sigma(t) > 2*t, print1(t, ", ")););} \\ up to the m-th triangular number; Michel Marcus, Mar 10 2013

Formula

Intersection of A000217 and A005101. - Michel Marcus, Mar 10 2013