id:A065655 - OEIS Search Results

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Composite numbers n such that to Sigma[n]*Phi[n]+2*(Sigma[n]) is a square.

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28, 90, 156, 184, 374, 1855, 2162, 2170, 2280, 2376, 2415, 2665, 3160, 4970, 5270, 5740, 6402, 6494, 7414, 8400, 9118, 10656, 11155, 12400, 14632, 14910, 15010, 15906, 18183, 18792, 22648, 24645, 24734, 24920, 25844, 26670, 27478, 28990 (list; graph; listen)

	OFFSET	`1,1`
	EXAMPLE	`Since (p+1)(p-1)+2(p+1) = pp+2p+1 = (p+1)^2 is a square, all primes were solutions. n = 28, sigma[28] = 56, phi[28] = 12, 56.12+2.56 = 784 = 28.28, so 28 is a composite solution.`
	CROSSREFS	`Cf. A000203, A000010.` `Adjacent sequences: A065652 A065653 A065654 this_sequence A065656 A065657 A065658` `Sequence in context: A042540 A042544 A042546 this_sequence A113958 A044215 A044596`
	KEYWORD	`nonn`
	AUTHOR	`Labos E, (labos(AT)ana.sote.hu), Nov 12 2001`

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Last modified October 13 20:18 EDT 2008. Contains 145016 sequences.

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