id:A109198 - OEIS Search Results

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Minimal value of k>0 such that n^3 + k^2 is semiprime.

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2, 3, 1, 8, 1, 2, 1, 8, 5, 4, 9, 4, 11, 2, 13, 2, 1, 12, 1, 12, 7, 5, 1, 2, 5, 3, 3, 10, 1, 18, 7, 4, 3, 2, 5, 2, 7, 2, 7, 2, 7, 6, 1, 2, 5, 7, 3, 4, 11, 2, 3, 16, 5, 2, 11, 2, 9, 2, 1, 40, 1, 4, 5, 8, 5, 9, 17, 2, 7, 5, 1, 6, 1, 4, 3, 14, 3, 4, 1, 18, 9, 10, 3, 6, 5, 3, 15, 4, 9, 3, 7, 10, 11, 2, 3, 12 (list; graph; listen)

	OFFSET	`0,1`
	COMMENT	`When n+1 and n^2+1 are both prime, then k=1.`
	FORMULA	`a(n) = minimal value of k>0 such that n^3 + k^2 is semiprime.`
	EXAMPLE	`a(0) = 2 because 0^3 + 1^2 = 1 is not semiprime, but 0^3 + 2^2 = 4 = 2^2 is.` `a(1) = 3 because 1^3 + 1^2 and 1^3 + 2^2 are not semiprime, but 1^3 + 3^2 = 10 = 2 * 5 is semiprime.` `a(59) = 40 because 59^3 + 40^2 = 206979 = 3 * 68993 and for no smaller k>0 is 59^3 + k^2 a semiprime.` `a(100) = 1 because 100^3 + 1^2 = 1000001 = 101 * 9901.`
	CROSSREFS	`Cf. A001358, A108714, A109197.` `Adjacent sequences: A109195 A109196 A109197 this_sequence A109199 A109200 A109201` `Sequence in context: A103364 A104027 A097710 this_sequence A081320 A011152 A078298`
	KEYWORD	`easy,nonn`
	AUTHOR	`Jonathan Vos Post (jvospost2(AT)yahoo.com), Jun 22 2005`

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

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