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 A316868 #16 Apr 26 2021 17:05:01 %S A316868 0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0, %T A316868 0,0,0,1,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,1, %U A316868 0,0,1,1,1,1,1,1,1,2,1,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0 %N A316868 Number of times 7 appears in decimal expansion of n. %e A316868 a(0) = 0 since the decimal representation of 0 does not contain the digit 7. %e A316868 a(7) = 1 since 7 appears once in the decimal expansion of 7. %t A316868 Array[ DigitCount[#, 10, 7] &, 105, 0] %o A316868 (PARI) a(n) = #select(x->x==7, digits(n)); \\ _Michel Marcus_, Jul 20 2018 %Y A316868 Cf. A043517, A043518, A043519, A043520. %Y A316868 Cf. A055641, A268643, A316863, A316864, A316865, A316866, A316867, A316869, A102683. %Y A316868 Cf. A079692. %K A316868 base,easy,nonn %O A316868 0,78 %A A316868 _Robert G. Wilson v_, Jul 15 2018