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 A045972 #14 Sep 19 2023 01:43:41
%S A045972 9,25,49,125,121,1225,169,625,343,3025,289,6125,361,4225,5929,3125,
%T A045972 529,8575,841,15125,8281,7225,961,30625,1331,9025,2401,21125,1369,
%U A045972 148225,1681,15625,14161,13225,20449,42875,1849,21025,17689,75625,2209,207025
%N A045972 a(1)=9; if n = Product p_i^e_i, n > 1, then a(n) = Product p_{i+2}^{e_i+1}.
%D A045972 From a puzzle proposed by _Marc LeBrun_.
%F A045972 Sum_{n>=1} 1/a(n) = (4/7) * (zeta(2)*zeta(3)/zeta(6)) - 8/9 = 0.221737646437... . - _Amiram Eldar_, Sep 19 2023
%t A045972 f[p_, e_] := NextPrime[p, 2]^(e + 1); a[1] = 9; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* _Amiram Eldar_, Sep 19 2023 *)
%Y A045972 Cf. A045965, A045966, A045967, A045968, A045969, A045970, A045971, A045973, A082695.
%K A045972 easy,nonn
%O A045972 1,1
%A A045972 _N. J. A. Sloane_
%E A045972 More terms from _David W. Wilson_