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A015705 Geometric mean of phi(n) and sigma(n) is an integer, n odd. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
Richard K. Guy, Divisors and desires, Amer. Math. Monthly, 104 (1997), 359-360.
PROG
(PARI) isok(n) = (n%2) && issquare(sigma(n)*eulerphi(n)); \\ Michel Marcus, Oct 02 2017
CROSSREFS
Cf. A011257.
Sequence in context: A160847 A260517 A235878 * A359088 A044238 A044619
KEYWORD
nonn
AUTHOR
EXTENSIONS
Offset corrected by Donovan Johnson, Jan 18 2012
STATUS
approved

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Last modified March 29 10:59 EDT 2024. Contains 371277 sequences. (Running on oeis4.)