A065523 - OEIS

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A065523

Numbers n such that sigma(n) is a prime power (A025475).

3, 7, 21, 31, 81, 93, 127, 217, 381, 400, 651, 889, 2667, 3937, 8191, 11811, 24573, 27559, 57337, 82677, 131071, 172011, 253921, 393213, 524287, 761763, 917497, 1040257, 1572861, 1777447, 2752491, 3120771, 3670009, 4063201, 5332341 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,1`
	LINKS	`Donovan Johnson, Table of n, a(n) for n = 1..80`
	MATHEMATICA	`s[n_] := DivisorSigma[1, n ]; Select[ Range[2, 10^6], !PrimeQ[ s[ # ]] && Mod[ s[ # ], s[ # ] - EulerPhi[ s[ # ]]] == 0 & ]`
	CROSSREFS	`A proper subset of A065496.` `Sequence in context: A018548 A003585 A108102 * A046528 A018572 A018641` `Adjacent sequences: A065520 A065521 A065522 * A065524 A065525 A065526`
	KEYWORD	`nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Nov 27 2001`
	EXTENSIONS	`a(31)-a(35) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Sep 05 2008`

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Last modified February 14 10:24 EST 2012. Contains 205614 sequences.