id:A108488 - OEIS Search Results

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Expansion of 1/sqrt(1-2x-3x^2-4x^3+4x^4).

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1, 1, 3, 9, 23, 69, 203, 601, 1815, 5493, 16731, 51225, 157367, 485093, 1499499, 4646233, 14427095, 44880981, 139849979, 436419737, 1363713015, 4266417221, 13362194571, 41891406681, 131452430999, 412835452213, 1297543367835 (list; graph; listen)

	OFFSET	`0,3`
	COMMENT	`In general, sum{k=0..n, C(n-k,k)^2a^kb^(n-k)} has expansion 1/sqrt(1-2bx-(2ab-b^2)x^2-2ab^2x^3+(ab)^2*x^4).`
	FORMULA	`a(n)=sum{k=0..n, C(n-k, k)^2*2^k}.`
	CROSSREFS	`Cf. A051286, A108480.` `Sequence in context: A164949 A146661 A004666 this_sequence A018334 A146392 A147508` `Adjacent sequences: A108485 A108486 A108487 this_sequence A108489 A108490 A108491`
	KEYWORD	`easy,nonn`
	AUTHOR	`Paul Barry (pbarry(AT)wit.ie), Jun 04 2005`

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Last modified December 5 17:24 EST 2009. Contains 170342 sequences.

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