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A015709
Composite n such that phi(n) * sigma(n) is one less than a square.
3
6, 22, 33, 44, 69, 76, 82, 140, 190, 295, 354, 392, 423, 451, 531, 581, 650, 944, 1072, 1119, 1142, 1150, 1668, 2276, 2893, 4043, 4163, 4176, 4192, 4257, 4262, 4509, 5090, 5975, 7260, 8660, 12977, 14927, 15026, 15753, 16064, 19105
OFFSET
1,1
LINKS
Richard K. Guy, Divisors and desires, Amer. Math. Monthly, 104 (1997), 359-360.
PROG
(PARI) isok(n) = !isprime(n) && issquare(eulerphi(n)*sigma(n)+1); \\ Michel Marcus, Oct 02 2017
CROSSREFS
Sequence in context: A296981 A035285 A069824 * A020195 A035134 A075799
KEYWORD
nonn
EXTENSIONS
Offset corrected by Donovan Johnson, Apr 02 2012
STATUS
approved