A103839 - OEIS

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A103839

Number of permutations of (1,2,3,...,n) where each of the (n-1) adjacent pairs of elements sums to a prime.

1, 2, 2, 8, 4, 16, 24, 60, 140, 1328, 2144, 17536, 23296, 74216, 191544, 2119632, 4094976, 24223424, 45604056, 241559918, 675603568, 8723487720, 22850057800, 285146572432 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	FORMULA	`For n>1, A103839(n)=2*A051239(n).`
	EXAMPLE	`For n = 5, we have the 4 permutations and the sums of adjacent elements:` `1,4,3,2,5 (1+4=5, 4+3=7, 3+2=5, 2+5=7)` `3,4,1,2,5 (3+4=7, 4+1=5, 1+2=3, 2+5=7)` `5,2,1,4,3 (5+2=7, 2+1=3, 1+4=5, 4+3=7)` `5,2,3,4,1 (5+2=7, 2+3=5, 3+4=7, 4+1=5)`
	CROSSREFS	`Sequence in context: A144847 A143625 A003612 * A135727 A075101 A075103` `Adjacent sequences: A103836 A103837 A103838 * A103840 A103841 A103842`
	KEYWORD	`nonn`
	AUTHOR	`N. J. A. Sloane (njas(AT)research.att.com), Mar 30 2005`
	EXTENSIONS	`More terms from Max Alekseyev, Jan 04 2008`

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Last modified February 13 04:08 EST 2012. Contains 205435 sequences.