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 A025693 #18 Jul 06 2025 13:24:06 %S A025693 1,2,3,5,7,9,12,15,18,22,26,30,35,40,45,51,57,64,71,78,86,94,102,111, %T A025693 120,129,139,149,159,170,181,193,205,217,230,243,256,270,284,298,313, %U A025693 328,343,359,375,392,409,426,444,462,480,499,518,537,557,577,597,618,639,661,683 %N A025693 Index of 2^n within sequence of numbers of form 2^i*7^j. %C A025693 Positions of zeros in A025664. - _R. J. Mathar_, Jul 06 2025 %H A025693 Charles R Greathouse IV, <a href="/A025693/b025693.txt">Table of n, a(n) for n = 0..10000</a> %F A025693 a(n) ~ kn^2 + O(n) with k = log(7)/log(2) - log(7)^2/log(2)^2. - _Charles R Greathouse IV_, Jun 28 2011 %o A025693 (PARI) a(n)=my(N=7<<n);sum(k=0,log(N)\log(7)-1,#binary(N\=7)) \\ _Charles R Greathouse IV_, Jun 28 2011 %o A025693 (PARI) a(n)=my(N=1); n+1+sum(i=1, n, logint(N<<=1, 7)); \\ _Charles R Greathouse IV_, Jan 11 2018 %o A025693 (PARI) first(n)=my(s, N=1/2); vector(n+1, i, s+=logint(N<<=1, 7)+1) \\ _Charles R Greathouse IV_, Jan 11 2018 %Y A025693 Cf. A003591. %K A025693 nonn,easy %O A025693 0,2 %A A025693 _David W. Wilson_ %E A025693 An incorrect g.f. was deleted by _N. J. A. Sloane_, Sep 16 2009