%I #12 Oct 02 2017 10:55:02

%S 6,22,44,76,82,140,190,354,392,650,944,1072,1142,1150,1668,2276,4176,

%T 4192,4262,5090,7260,8660,15026,16064,22926,29746,39436,42872,74666,

%U 87498,94786,101882,115772,118928,127580,151348

%N Composite and even n such that phi(n) * sigma(n) is one less than a square.

%H Donovan Johnson, <a href="/A015721/b015721.txt">Table of n, a(n) for n = 1..300</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) = !isprime(n) && !(n%2) && issquare(eulerphi(n)*sigma(n)+1); \\ _Michel Marcus_, Oct 02 2017

%Y Subsequence of even terms of A015709.

%K nonn

%O 1,1

%A _Robert G. Wilson v_

%E Offset corrected by _Donovan Johnson_, Jan 16 2012