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Search: id:A055217
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| A055217 |
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a(n) = sum of the first n coefficients of (1+x+x^2)^n. |
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+0
2
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| 1, 3, 10, 31, 96, 294, 897, 2727, 8272, 25048, 75747, 228826, 690691, 2083371, 6280650, 18925047, 57002616, 171633840, 516632307, 1554702516, 4677501237, 14069962041, 42314975352, 127240600050, 382555886571, 1150026301089
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OFFSET
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0,2
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FORMULA
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Binomial transform of A117186; g.f.: (1+x-sqrt(1-2x-3x^2))/(2x(1-2x-3x^2)); a(n)=(3^(n+1)+A002426(n+1))/2; - Paul Barry (pbarry(AT)wit.ie), Jan 20 2008
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CROSSREFS
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T(2n+1, n), array T as in A055216.
Sequence in context: A136853 A033121 A106517 this_sequence A097472 A068094 A100058
Adjacent sequences: A055214 A055215 A055216 this_sequence A055218 A055219 A055220
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KEYWORD
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nonn
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AUTHOR
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Clark Kimberling (ck6(AT)evansville.edu), May 07 2000
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EXTENSIONS
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New description from Paul D. Hanna (pauldhanna(AT)juno.com), Oct 09 2003
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