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 A151780 #19 Nov 17 2022 05:26:54 %S A151780 1,1,5,1,5,5,25,1,5,5,25,5,25,25,125,1,5,5,25,5,25,25,125,5,25,25,125, %T A151780 25,125,125,625,1,5,5,25,5,25,25,125,5,25,25,125,25,125,125,625,5,25, %U A151780 25,125,25,125,125,625,25,125,125,625,125,625,625,3125,1,5,5,25,5,25,25,125,5 %N A151780 a(n) = 5^(wt(n) - 1) where wt(n) = A000120(n). %e A151780 From _Omar E. Pol_, Jul 21 2009: (Start) %e A151780 If written as a triangle: %e A151780 1; %e A151780 1,5; %e A151780 1,5,5,25; %e A151780 1,5,5,25,5,25,25,125; %e A151780 1,5,5,25,5,25,25,125,5,25,25,125,25,125,125,625; %e A151780 1,5,5,25,5,25,25,125,5,25,25,125,25,125,125,625,5,25,25,125,25,125,125,625,... %e A151780 (End) %o A151780 (Python 3.10+) %o A151780 def A151780(n): return 5**(n.bit_count()-1) # _Chai Wah Wu_, Nov 15 2022 %o A151780 (PARI) a(n) = 5^(hammingweight(n)-1); \\ _Michel Marcus_, Nov 15 2022 %Y A151780 Essentially A151779/6. %Y A151780 Cf. A000120, A048881, A048896, A147610, A151783. %Y A151780 Cf. A000351. - _Omar E. Pol_, Jul 21 2009 %K A151780 nonn %O A151780 1,3 %A A151780 _N. J. A. Sloane_, Jun 25 2009