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 A262481 #16 Jul 24 2023 02:35:43 %S A262481 1,6,10,12,18,20,21,24,34,36,40,48,55,66,68,69,72,80,81,96,115,130, %T A262481 132,136,144,155,160,185,192,205,258,260,261,264,272,273,288,295,320, %U A262481 321,355,384,395,425,514,516,520,528,535,544,565,576,595,623,625,637 %N A262481 Numbers m having in binary representation exactly lpf(m) ones, where lpf = least prime factor = A020639; a(1) = 1. %H A262481 Reinhard Zumkeller, <a href="/A262481/b262481.txt">Table of n, a(n) for n = 1..10000</a> %F A262481 A000120(a(n)) = A020639(a(n)). %e A262481 . n | a(n) | A007088(a(n)) | factorization %e A262481 . ----+------+---------------+-------------- %e A262481 . 1 | 1 | 1 | 1 %e A262481 . 2 | 6 | 110 | 2 * 3 %e A262481 . 3 | 10 | 1010 | 2 * 5 %e A262481 . 4 | 12 | 1100 | 2^2 * 3 %e A262481 . 5 | 18 | 10010 | 2 * 3^2 %e A262481 . 6 | 20 | 10100 | 2^2 * 5 %e A262481 . 7 | 21 | 10101 | 3 * 7 %e A262481 . 8 | 24 | 11000 | 2^3 * 3 %e A262481 . 9 | 34 | 100010 | 2 * 17 %e A262481 . 10 | 36 | 100100 | 2^2 * 3^2 %e A262481 . 11 | 40 | 101000 | 2^3 * 5 %e A262481 . 12 | 48 | 110000 | 2^4 * 3 %e A262481 . 13 | 55 | 110111 | 5 * 11 %e A262481 . 14 | 66 | 1000010 | 2 * 3 * 11 %e A262481 . 15 | 68 | 1000100 | 2^2 * 17 %e A262481 . 16 | 69 | 1000101 | 3 * 23 %e A262481 . 17 | 72 | 1001000 | 2^3 * 3^2 %e A262481 . 18 | 80 | 1010000 | 2^4 * 5 %e A262481 . 19 | 81 | 1010001 | 3^4 %e A262481 . 20 | 96 | 1100000 | 2^5 * 3 %e A262481 . 21 | 115 | 1110011 | 5 * 23 %e A262481 . 22 | 130 | 10000010 | 2 * 5 * 13 %e A262481 . 23 | 132 | 10000100 | 2^2 * 3 * 11 %e A262481 . 24 | 136 | 10001000 | 2^3 * 17 %e A262481 . 25 | 144 | 10010000 | 2^4 * 3^2 . %t A262481 Select[Range[640], FactorInteger[#][[1, 1]] == DigitCount[#, 2, 1] &] (* _Amiram Eldar_, Jul 24 2023 *) %o A262481 (Haskell) %o A262481 a262481 n = a262481_list !! (n-1) %o A262481 a262481_list = filter (\x -> a000120 x == a020639 x) [1..] %o A262481 (PARI) isok(n) = (n==1) || (hammingweight(n) == factor(n)[1,1]); \\ _Michel Marcus_, Sep 29 2015 %Y A262481 Cf. A000120, A020639, A007088. %Y A262481 Subsequence of A052294. %K A262481 nonn,base %O A262481 1,2 %A A262481 _Reinhard Zumkeller_, Sep 24 2015