id:A089653 - OEIS Search Results

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(Product of prime factors of n) - 1 is a perfect square.

+0
4

2, 4, 5, 8, 10, 16, 17, 20, 25, 26, 32, 37, 40, 50, 52, 64, 65, 80, 82, 100, 101, 104, 122, 125, 128, 145, 160, 164, 170, 197, 200, 208, 226, 244, 250, 256, 257, 289, 290, 320, 325, 328, 338, 340, 362, 400, 401, 416, 442, 452, 485, 488, 500, 512, 530, 577, 580 (list; graph; listen)

	OFFSET	`1,1`
	EXAMPLE	`The prime factors of 10 are 2 and 5 and 2 * 5 - 1 = 9 is a square; so 10 belongs to the sequence.`
	MATHEMATICA	`ppf[n_] := Apply[Times, Transpose[FactorInteger[n]][[1]]]; Select[Range[2, 10^3], IntegerQ[Sqrt[ppf[ # ] - 1]] &]`
	CROSSREFS	`Cf. A089632. A091419 gives squares, A091420 gives square roots.` `Sequence in context: A105425 A032937 A126684 this_sequence A114652 A067943 A067937` `Adjacent sequences: A089650 A089651 A089652 this_sequence A089654 A089655 A089656`
	KEYWORD	`nonn`
	AUTHOR	`Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 04 2004`

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.

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