id:A063531 - OEIS Search Results

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Sigma[n]+1 is a square.

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2, 7, 8, 14, 15, 23, 32, 33, 35, 47, 54, 56, 57, 60, 72, 78, 79, 84, 87, 92, 95, 120, 123, 124, 128, 138, 143, 154, 165, 167, 174, 184, 190, 196, 213, 223, 235, 242, 252, 253, 258, 267, 295, 312, 315, 319, 323, 327, 348, 359, 375, 378, 380, 393, 412, 423, 439 (list; graph; listen)

	OFFSET	`1,1`
	FORMULA	`A000203[x]=-1+m^2 fore some m.`
	EXAMPLE	`If n = p(p+2) is a product of twin primes (from A037074), then Sigma[n]+1 = 1+(p+1)(p+3) = (p+2)^2, square of the larger twin. Other solutions can be either special primes = -2+x^2 or composites like 120: Sigma[120] = 120+60+...+1 = 360 = -1+19^2. Square number solution is e.g. 196: 1+Sigma[196] = 399 = -1+20^2.`
	CROSSREFS	`A000010, A000203, A037074, A015722.` `Sequence in context: A047239 A032927 A004717 this_sequence A063771 A064293 A063729` `Adjacent sequences: A063528 A063529 A063530 this_sequence A063532 A063533 A063534`
	KEYWORD	`nonn`
	AUTHOR	`Labos E. (labos(AT)ana.sote.hu), Aug 02 2001`

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Last modified November 30 22:12 EST 2008. Contains 150989 sequences.

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