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 A255342 #11 Apr 30 2015 21:15:51
%S A255342 3,7,8,11,15,21,25,26,29,30,34,37,38,41,43,44,47,51,55,56,59,63,69,75,
%T A255342 79,80,83,87,93,99,103,104,107,111,117,121,122,125,126,130,133,134,
%U A255342 137,139,140,143,144,148,156,160,162,166,169,170,173,174,178,181,182,185,187,188,191,193,194,197,198,202
%N A255342 Numbers n such that there are exactly two 1's in their factorial base representation (A007623).
%H A255342 Antti Karttunen, <a href="/A255342/b255342.txt">Table of n, a(n) for n = 1..13132</a>
%e A255342 The factorial base representation (A007623) of 3 is "11", which contains exactly two 1's, thus 3 is included in the sequence.
%e A255342 The f.b.r. of 7 is "101", with exactly two 1's, thus 7 is included in the sequence.
%e A255342 The f.b.r. of 21 is "311", with exactly two 1's, thus 21 is included in the sequence.
%t A255342 factBaseIntDs[n_] := Module[{m, i, len, dList, currDigit}, i = 1; While[n > i!, i++]; m = n; len = i; dList = Table[0, {len}]; Do[currDigit = 0; While[m >= j!, m = m - j!; currDigit++]; dList[[len - j + 1]] = currDigit, {j, i, 1, -1}]; If[dList[[1]] == 0, dList = Drop[dList, 1]]; dList]; s = Table[FromDigits[factBaseIntDs[n]], {n, 240}]; Flatten@ Position[s, x_ /; DigitCount[x][[1]] == 2](* _Michael De Vlieger_, Apr 27 2015, after _Alonso del Arte_ at A007623 *)
%o A255342 (Scheme, with _Antti Karttunen_'s IntSeq-library)
%o A255342 (define A255342 (MATCHING-POS 1 0 (lambda (n) (= 2 (A257511 n)))))
%Y A255342 Cf. A007623, A257511, A255411, A255341, A255343.
%Y A255342 Subsequence of A256450.
%Y A255342 Subsequence: A038507 (apart from its initial 2 terms).
%K A255342 nonn,base
%O A255342 1,1
%A A255342 _Antti Karttunen_, Apr 27 2015