A015705 Geometric mean of phi(n) and sigma(n) is an integer, n odd.

1, 51, 105, 405, 477, 595, 679, 1023, 1455, 1463, 1485, 1715, 1731, 2651, 2945, 3135, 3567, 4381, 5797, 5859, 8245, 8255, 8721, 9639, 9809, 10127, 10153, 10179, 10295, 11935, 12369, 17765, 17955, 19125, 19875, 20195, 20213, 20273

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

Links

• Donovan Johnson, Table of n, a(n) for n = 1..10000
• Richard K. Guy, Divisors and desires, Amer. Math. Monthly, 104 (1997), 359-360.

Crossrefs

Cf. A011257.

Programs

PARI

isok(n) = (n%2) && issquare(sigma(n)*eulerphi(n)); \\ Michel Marcus, Oct 02 2017

Extensions

Offset corrected by Donovan Johnson, Jan 18 2012