This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A139116 #13 Oct 18 2024 11:41:55 %S A139116 1,3,10,21,78,136,171,465,1830,3916,5671,8001,135460,183921,817281, %T A139116 2425503,2600340,5172936,9041878,9779253,46933516,49406770,62860078, %U A139116 198732016,235455850,269317236,989969256,3718884403,6105401253,8718403176,23347552095,286402257541 %N A139116 a(n) = p*(p-1)/2, where p is A000043(n). %H A139116 Amiram Eldar, <a href="/A139116/b139116.txt">Table of n, a(n) for n = 1..48</a> (terms 1..47 from Harvey P. Dale) %F A139116 a(n) = A000043(n)*(A000043(n)-1)/2. %t A139116 (#(#-1))/2&/@MersennePrimeExponent[Range[47]] (* _Harvey P. Dale_, Aug 13 2021 *) %Y A139116 Cf. A000043, A000217, A036689, A139306, A139307, A139116, A139223, A139224, A139225, A139226. %K A139116 nonn %O A139116 1,2 %A A139116 _Omar E. Pol_, May 10 2008 %E A139116 a(24)-a(32) from _Harvey P. Dale_, Aug 13 2021