A115120 - OEIS

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A115120

Number of imprimitive (periodic) 2n-bead black-white reversible necklaces with n black beads.

0, 0, 1, 1, 2, 1, 4, 1, 8, 3, 17, 1, 56, 1, 134, 18, 440, 1, 1434, 1, 4758, 135, 16160, 1, 57254, 16 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,5`
	COMMENTS	`a(p)=1 for prime p.`
	FORMULA	`a(n)=A005648(n) - A0045628(n).`
	CROSSREFS	`Sequence in context: A097360 A072345 A200583 * A147373 A147441 A146269` `Adjacent sequences: A115117 A115118 A115119 * A115121 A115122 A115123`
	KEYWORD	`easy,nonn`
	AUTHOR	`Valery A. Liskovets (liskov(AT)im.bas-net.by), Jan 17 2006`

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Last modified February 14 02:39 EST 2012. Contains 205567 sequences.