|
%I #15 Jul 21 2017 17:28:28
%S 1811079,4473387,67009923,77242167,88605819,110475819,120781449,
%T 132208767,134082297,165515319,183408867,225548469,232275681,
%U 272876607,284339403,326557251,349538247,402371793,425844621,501668883,566867727
%N Year numbers, i.e., phi(n) = 2 phi(sigma(n)), divisible by a 5th prime power.
%C See A137815 for more comments and references about "year numbers". This is the subsequence of elements of A137815 divisible by a 5th prime power. As such, it is of course also a subsequence of A137818 (those divisible by a 4th prime power).
%C There are only 5 such numbers below 10^8.
%H Donovan Johnson, <a href="/A137819/b137819.txt">Table of n, a(n) for n = 1..100</a>
%o (PARI) for( i=1,#A137816, vecmax(factor(A137816[i])[,2])>4 & print1(A137816[i])", ")
%o (PARI) for( n=1,10^9, issquarefree(n) && next; vecmax(factor(n)[,2])>4 || next; eulerphi(n)==2*eulerphi(sigma(n)) && print1(n", "))
%Y Cf. A137815-A137818.
%K nonn
%O 1,1
%A _R. K. Guy_, _R. J. Mathar_ and _M. F. Hasler_, Feb 11 2008
%E More terms from Russell Pochis (joebobpumpkin(AT)gmail.com), May 30 2010
%E Typo in data corrected by _D. S. McNeil_, Aug 17 2010
|
