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A118334
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a(n-1)*a(n-6) + a(n-2)*a(n-7) + a(n-3)*a(n-8) + a(n-4)*a(n-9), with a(k<8) = 1.
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1
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1, 1, 1, 1, 1, 1, 1, 1, 4, 7, 13, 25, 49, 94, 463, 3691, 51649, 1342825, 67140874, 6378379789, 2959568174113, 10926725697533971, 564365382277563803725, 757844508822251885989584694, 50882343436271211095738004051924943
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OFFSET
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0,9
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COMMENTS
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This is the 4-term analog of the 2-term recurrence A111288 a(1) = a(2) = a(3) = a(4) = 1. For n>= 5, a(n) = a(n-1)*a(n-3) + a(n-2)*a(n-4). Primes in this sequence include a(n) for n = 9, 10, 14, 15... with a(16) through a(28) composite, a(28) has 74 digits and the sequence growing beyond my ability to efficiently test primality.
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LINKS
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Harvey P. Dale, Table of n, a(n) for n = 0..37
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FORMULA
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a(0) = a(1) = a(2) = a(3) = a(4) = a(5) = a(6) = a(7) = 1; for n>7: a(n) = a(n-1)*a(n-6) + a(n-2)*a(n-7) + a(n-3)*a(n-8) + a(n-4)*a(n-9).
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MATHEMATICA
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nxt[{a_, b_, c_, d_, e_, f_, g_, h_, i_}]:={b, c, d, e, f, g, h, i, Total[ {a*f+ b*g+ c*h+ d*i}]}; Transpose[NestList[nxt, {1, 1, 1, 1, 1, 1, 1, 1, 1}, 30]][[1]] (* Harvey P. Dale, Aug 21 2014 *)
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CROSSREFS
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Cf. A111288, A111388.
Sequence in context: A229439 A000288 A074863 * A205538 A181565 A004119
Adjacent sequences: A118331 A118332 A118333 * A118335 A118336 A118337
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post, May 14 2006
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STATUS
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approved
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