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 A245431 #11 Jul 22 2014 12:34:25 %S A245431 10,10,10,20,30,40,60,80,120,170,240,340,490,700,1000,1430,2040,2910, %T A245431 4160,5940,8490,12130,17330,24750,35360,50520,72170,103100,147280, %U A245431 210400,300570,429390,613410,876300,1251860,1788370,2554820,3649740,5213910,7448450 %N A245431 Number of nonnegative integers with property that their base 10/7 expansion has n digits. %C A245431 See A024662 for an explanation of base 10/7. %e A245431 a(2) = 10 because 70, 71, 72, 73, 74, 75, 76, 77, 78 and 79 are the base 10/7 expansions for the integers 10, 11, 12, 13, 14, 15, 16, 17, 18 and 19 respectively and these are the only integers with 2 digits. %o A245431 (Sage) %o A245431 A=[1] %o A245431 for i in [1..60]: %o A245431 A.append(ceil(((10-7)/7)*sum(A))) %o A245431 [10*x for x in A] %Y A245431 Cf. A024662, A081848, A245356. %K A245431 nonn,base %O A245431 1,1 %A A245431 _Hailey R. Olafson_, Jul 21 2014