|
%I #13 Oct 02 2017 10:54:42
%S 1,51,105,405,477,595,679,1023,1455,1463,1485,1715,1731,2651,2945,
%T 3135,3567,4381,5797,5859,8245,8255,8721,9639,9809,10127,10153,10179,
%U 10295,11935,12369,17765,17955,19125,19875,20195,20213,20273
%N Geometric mean of phi(n) and sigma(n) is an integer, n odd.
%H Donovan Johnson, <a href="/A015705/b015705.txt">Table of n, a(n) for n = 1..10000</a>
%H Richard K. Guy, <a href="http://www.jstor.org/stable/2974586">Divisors and desires</a>, Amer. Math. Monthly, 104 (1997), 359-360.
%o (PARI) isok(n) = (n%2) && issquare(sigma(n)*eulerphi(n)); \\ _Michel Marcus_, Oct 02 2017
%Y Cf. A011257.
%K nonn
%O 1,2
%A _Robert G. Wilson v_
%E Offset corrected by _Donovan Johnson_, Jan 18 2012
|
