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 A121315 #14 Mar 20 2015 05:25:45
%S A121315 2,6,12,20,35,56,72,99,143,208,272,323,437,575,675,783,899,992,1184,
%T A121315 1517,1763,2021,2303,2597,3127,3599,3904,4288,4757,5183,5767,6399,
%U A121315 6723,7387,8633,9797,10403,11021,11663,12317,13673,15125,15875,16256,16768
%N A121315 Products of two consecutive prime powers.
%C A121315 For some algorithms for finding A034699(n), the numbers in this sequence represent a worst-case scenario of execution time.
%F A121315 a(n) = A000961(n)*A000961(n+1).
%e A121315 437 = 19*23 and none of the intervening integers (20,21,22) are prime powers.
%t A121315 t = Join[{1}, Select[Range[2, 131], Mod[ #, # - EulerPhi[ # ]] == 0 &]]; Most@t*Rest@t (* _Robert G. Wilson v_, Sep 02 2006 *)
%o A121315 (PARI) lista(nn) = v = concat(1, select(x->isprimepower(x), vector(nn, n, n))); for (n=1, #v-1, print1(v[n]*v[n+1], ", ")); \\ _Michel Marcus_, Mar 20 2015
%Y A121315 Cf. A000961, A034699.
%K A121315 nonn
%O A121315 1,1
%A A121315 _Paul Richards_, Aug 28 2006
%E A121315 More terms from _Robert G. Wilson v_, Sep 02 2006