Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #11 Dec 15 2017 17:36:06
%S 3,21,105,325,7875,9568125
%N Triangular numbers whose sum of primes from smallest to largest prime factor is triangular and whose sum of composites from smallest to largest prime factor is triangular.
%C No more terms < 2.77*10^12. - _David Wasserman_, Jul 20 2005
%C a(7) > 2*10^15. - _Donovan Johnson_, Feb 03 2013
%e 325 = 5^2*13, sum of primes between: 5+7+11+13 = 36, triangular; sum of composites between: 6+8+9+10+12 = 45, triangular.
%Y Cf. A000217, A074036, A074037.
%K more,nonn
%O 1,1
%A _Jason Earls_, Nov 02 2002
%E Offset corrected by _Donovan Johnson_, Feb 03 2013