A089928 - OEIS

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A089928

a(n)=2a(n-1)+2a(n-3)+a(n-4).

1, 2, 4, 10, 25, 60, 144, 348, 841, 2030, 4900, 11830, 28561, 68952, 166464, 401880, 970225, 2342330, 5654884, 13652098, 32959081, 79570260, 192099600, 463769460, 1119638521, 2703046502, 6525731524, 15754509550, 38034750625, 91824010800 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,2`
	LINKS	`Index entries for sequences related to Chebyshev polynomials.`
	FORMULA	`a(n)=(-i)^nsum{k=0..floor(n/2), U(n-2k, i)} with i^2=-1; a(n)=(sqrt(2)+1)^n(3+2sqrt(2))/8+(sqrt(2)-1)^n(3-2sqrt(2))/8+(-1)^n/4.`
	CROSSREFS	`Cf. A006498.` `Sequence in context: A148091 A123420 A000458 * A173610 A036887 A151536` `Adjacent sequences: A089925 A089926 A089927 * A089929 A089930 A089931`
	KEYWORD	`easy,nonn`
	AUTHOR	`Paul Barry (pbarry(AT)wit.ie), Nov 15 2003`

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Last modified February 17 08:44 EST 2012. Contains 205998 sequences.