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 A357750 #21 Jan 03 2025 18:39:46 %S A357750 0,5,11,21,45,75,217,331,181,789,1241,2505,5701,5221,11309,19637, %T A357750 43151,69451,82709,166027,346389,607307,689685,1458357,1380917, %U A357750 2507541,5906699,2965685,5931189,11862197,47448787,82188309,57804981,94905541,188883211,373457573,640164021 %N A357750 a(n) is the least k such that B(k^2) - B(k) = n, where B(m) is the binary weight A000120(m). %e A357750 ---------------------------------------------------- %e A357750 n k k^2 binary k binary k^2 %e A357750 ---------------------------------------------------- %e A357750 0 0 0 0 0 %e A357750 1 5 25 101 11001 %e A357750 2 11 121 1011 1111001 %e A357750 3 21 441 10101 110111001 %e A357750 4 45 2025 101101 11111101001 %e A357750 5 75 5625 1001011 1010111111001 %e A357750 6 217 47089 11011001 1011011111110001 %e A357750 7 331 109561 101001011 11010101111111001 %e A357750 8 181 32761 10110101 111111111111001 %e A357750 9 789 622521 1100010101 10010111111110111001 %o A357750 (PARI) a(n) = my(k=0); while(hammingweight(k^2) - hammingweight(k) != n, k++); k; %o A357750 (Python) %o A357750 from itertools import count %o A357750 def A357750(n): %o A357750 for k in count(0): %o A357750 if (k**2).bit_count()-k.bit_count()==n: %o A357750 return k # _Chai Wah Wu_, Oct 17 2022 %Y A357750 Cf. A000120, A000290, A159918, A164343, A164344, A356877, A357658. %K A357750 nonn,base %O A357750 0,2 %A A357750 _Karl-Heinz Hofmann_ and _Hugo Pfoertner_, Oct 17 2022