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 A090881 #6 Oct 09 2013 14:20:16 %S A090881 0,1,4,2,16,5,64,3,8,17,256,6,1024,65,20,4,4096,9,16384,18,68,257, %T A090881 65536,7,32,1025,12,66,262144,21,1048576,5,260,4097,80,10,4194304, %U A090881 16385,1028,19,16777216,69,67108864,258,24,65537,268435456,8,128,33,4100,1026 %N A090881 Suppose n=(p1^e1)(p2^e2)... where p1,p2,... are the prime numbers and e1,e2,... are nonnegative integers. Then a(n) = e1 + (e2)*4 + (e3)*16 + (e4)*64 + ... + (ek)*(4^(k-1)) + ... %C A090881 Replace "4" with "x" and extend the definition of a to positive rationals and a becomes an isomorphism between positive rationals under multiplication and polynomials over Z under addition. This remark generalizes A001222, A048675 and A054841: evaluate said polynomial at x=1, x=2 and x=10, respectively. %D A090881 Joseph J. Rotman, The Theory of Groups: An Introduction, 2nd ed. Boston: Allyn and Bacon, Inc. 1973. Page 9, problem 1.26. %H A090881 Sam Alexander, <a href="http://tinyurl.com/yzjw">Post to sci.math</a>. %Y A090881 Cf. A001222, A048675, A054841, A090880, A090882, A090883, A090884. %K A090881 easy,nonn %O A090881 1,3 %A A090881 _Sam Alexander_, Dec 12 2003 %E A090881 More terms from _Ray Chandler_, Dec 20 2003