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 A387418 #6 Sep 01 2025 11:24:04
%S A387418 1,3,7,15,31,63,127,255,511,1023,1791,2047,2431,4095,8191,14335,14847,
%T A387418 16383,27391,32767,44031,57855,65535,114687,131071,204799,262143,
%U A387418 376831,524287,923647,1048575,1632255,2056191,2097151,2744319,4194303,6815743,8388607,8781823,8978431,12058623,16777215,19922943,24068095
%N A387418 Numbers k such that the odd part of (1+k) divides (1 + odd part of A034448(k)), where A034448 is unitary sigma (usigma).
%C A387418 Like in many sequences of this type, the criterion seems to strongly select for numbers with a long tail of trailing 1-bits. The initial 1 is probably the only term that is not in A004767.
%o A387418 (PARI)
%o A387418 A000265(n) = (n>>valuation(n,2));
%o A387418 A034448(n) = { my(f=factorint(n)); prod(k=1, #f~, 1+(f[k, 1]^f[k, 2])); };
%o A387418 isA387418(n) = !((1+A000265(A034448(n)))%A000265(1+n));
%Y A387418 Cf. A000225 (subsequence), A000265, A002827, A004767, A034448.
%Y A387418 For similar sequences, see A336700, A387410, A387415, A387419.
%K A387418 nonn,new
%O A387418 1,2
%A A387418 _Antti Karttunen_, Sep 01 2025