A074315 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

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

FORMULA

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

EXAMPLE

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.

MATHEMATICA

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

PROG

(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

CROSSREFS

Cf. A000217, A005101.

Sequence in context: A272190 A060671 A269499 * A240520 A126789 A176623

Adjacent sequences: A074312 A074313 A074314 * A074316 A074317 A074318

KEYWORD

nonn

AUTHOR

Shyam Sunder Gupta, Sep 22 2002

STATUS

approved