id:A113508 - OEIS Search Results

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Pentagon-free numbers.

+0
4

2, 3, 4, 6, 7, 8, 9, 11, 13, 14, 16, 17, 18, 19, 21, 23, 26, 27, 28, 29, 31, 32, 33, 34, 37, 38, 39, 41, 42, 43, 46, 47, 49, 52, 53, 54, 56, 57, 58, 59, 61, 62, 63, 64, 66, 67, 68, 69, 71, 73, 74, 76, 77, 79, 81, 82, 83, 86, 87, 89, 91, 93, 94, 97, 98, 99, 101 (list; graph; listen)

	OFFSET	`1,1`
	COMMENT	`Pentagonal number analogy of A112886 (the triangle-free positive integers).`
	FORMULA	`{a(n)} = {integers k>1: no divisor of k is a pentagonal number n(3n-1)/2}>1}. {a(n)} = {integers k>1: no divisor of k is an element of A000326 > 1}.`
	EXAMPLE	`10 is not an element, since 10 = 2 * 5 and 5 is the first nontrivial pentagonal number. 24 is not an element, since 12\|24 and 12 is a pentagonal number. 44 is not an element, since 22\|44 and 22 is a pentagonal number.`
	CROSSREFS	`Cf. A000326, A112886, A113502.` `Sequence in context: A140467 A103677 A087919 this_sequence A059325 A004763 A030706` `Adjacent sequences: A113505 A113506 A113507 this_sequence A113509 A113510 A113511`
	KEYWORD	`easy,nonn`
	AUTHOR	`Jonathan Vos Post (jvospost3(AT)gmail.com), Jan 11 2006`

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Last modified November 27 22:38 EST 2009. Contains 167602 sequences.

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