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 A137818 #9 Mar 28 2014 02:28:56 %S A137818 295569,1811079,1964375,2069469,4473387,5854375,10936053,13260625, %T A137818 18029709,21576537,22182093,25536875,35595625,46404333,49648383, %U A137818 55094375,57044817,58650625,67009923,69166467,72681875,76106875 %N A137818 Non-biquadratefree "year numbers": phi(n) = 2 phi(sigma(n)) and p^4 | n for some p>1. %C A137818 See A137815 for general comments and references about "year numbers". This is the subsequence of elements of A137815 divisible by a biquadrateful number, i.e. its intersection with A046101 (numbers divisible by the 4th power of some prime). As such, it is of course also a subsequence of A137817 and a fortiori of A137816. %C A137818 There are only 28 such numbers below 10^8. %H A137818 Donovan Johnson, <a href="/A137818/b137818.txt">Table of n, a(n) for n = 1..500</a> %o A137818 (PARI) for( i=1,#A137816, vecmax( factor( A137816[i])[,2])>3 && print1(A137816[i]", ")) %o A137818 (PARI) for( i=1,#A046099, eulerphi(A046099[i])==2*eulerphi(sigma(A046099[i])) && print1( A046099[i] ", ")) %o A137818 (PARI) for( n=1,10^9, issquarefree(n) && next; vecmax(factor(n)[,2])>3 || next; eulerphi(n)==2*eulerphi(sigma(n)) && print1(n", ")) %Y A137818 Cf. A137815-A137819, A046101. %K A137818 nonn %O A137818 1,1 %A A137818 _R. K. Guy_, _R. J. Mathar_ and _M. F. Hasler_, Feb 11 2008