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A115120 Number of imprimitive (periodic) 2n-bead black-white reversible necklaces with n black beads. +0
1
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; listen)
OFFSET

0,5

COMMENT

a(p)=1 for prime p.

FORMULA

a(n)=A005648(n) - A0045628(n).

CROSSREFS

Sequence in context: A115122 A097360 A072345 this_sequence A147373 A147441 A146269

Adjacent sequences: A115117 A115118 A115119 this_sequence 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 December 11 12:57 EST 2009. Contains 170656 sequences.


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