id:A143539 - OEIS Search Results

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Number of ways to express 2n-1 as p+2a^2; p prime, a > 0.

+0
5

0, 0, 1, 1, 1, 1, 2, 2, 0, 2, 3, 1, 3, 1, 1, 3, 1, 2, 3, 3, 1, 2, 3, 1, 4, 2, 1, 5, 1, 1, 5, 3, 1, 2, 4, 1, 3, 4, 2, 5, 3, 1, 4, 2, 2, 6, 2, 1, 3, 2, 3, 5, 4, 1, 5, 5, 1, 6, 3, 2, 5, 1, 2, 2, 4, 3, 5, 4, 0, 7, 4, 1, 6, 3, 1, 5, 2, 2, 5, 6, 1, 2, 5, 2, 7, 4, 2, 6, 2, 2, 9, 2, 3, 4, 4, 2, 2, 4, 1, 9, 5, 3, 5, 5, 3 (list; graph; listen)

	OFFSET	`1,7`
	COMMENT	`Similar to A046921 and A046923. Sequence A060003 lists the odd numbers having no representations.`
	LINKS	`T. D. Noe, Table of n, a(n) for n=1..10000` `L. Hodges, A lesser-known Goldbach conjecture, Math. Mag., 66 (1993), 45-47.`
	EXAMPLE	`a(11)=3 because 21 = 19+21^2 = 13+22^2 = 3+2*3^2.`
	MATHEMATICA	`Table[cnt=0; Do[If[PrimeQ[n-2*k^2], cnt++ ], {k, Floor[Sqrt[n/2]]}]; cnt, {n, 1, 20000, 2}]`
	CROSSREFS	`Sequence in context: A153239 A141661 A080769 this_sequence A099307 A072738 A165316` `Adjacent sequences: A143536 A143537 A143538 this_sequence A143540 A143541 A143542`
	KEYWORD	`nonn`
	AUTHOR	`T. D. Noe (noe(AT)sspectra.com), Aug 23 2008`

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Last modified December 11 12:57 EST 2009. Contains 170656 sequences.

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