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 A181960 #30 Aug 11 2015 09:49:55 %S A181960 9,40,156,740,3668,16948,77861,379084,1889419 %N A181960 Number of distinct nonnegative integers that can be generated by an expression containing n binary operators (any of add, subtract, multiply and divide) whose operands are any integer between 1 and 9; parenthesis allowed. %H A181960 Derek M. Jones, <a href="/A181960/a181960_1.r.txt">R program to calculate values</a> %H A181960 <a href="/index/Com#complexity">Index to sequences related to the complexity of n</a> %e A181960 a(1)=40, the distinct values are: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 20 21 24 25 27 28 30 32 35 36 40 42 45 48 49 54 56 63 64 72 81 %Y A181960 Cf. A181898, A181957, A181958, A181959. %K A181960 nonn,more %O A181960 0,1 %A A181960 _Derek M. Jones_, Apr 03 2012