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A140295
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a(n)=a(n-1)+a(n-2)+2a(n-3).
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1
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1, -2, 4, 4, 4, 16, 28, 52, 112, 220, 436, 880, 1756, 3508, 7024, 14044, 28084, 56176, 112348, 224692, 449392, 898780, 1797556, 3595120, 7190236, 14380468, 28760944, 57521884, 115043764, 230087536, 460175068, 920350132, 1840700272, 3681400540
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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FORMULA
| a(n+1)-2a(n)= period 3: repeat -4, 8, -4 .
a(n) = (3/7)*2^n+[(6/7)*I]*sqrt(3)*{-1/2+[(1/2)*I]*sqrt(3)}^n+(2/7)*{-1/2-[(1/2)*I]*sqrt(3)}^n+(2 /7)*{-1/2+[(1/2)*I]*sqrt(3)}^n-[(6/7)*I]*sqrt(3)*{-1/2-[(1/2)*I]*sqrt(3)}^n, with n>=0 and I=sqrt(-1) - Paolo P. Lava (paoloplava(AT)gmail.com), Jun 06 2008
G.f.: (1-3x+5x^2)/((1-2x)(1+x+x^2)). a(n)=(4*k(n)+3*2^n)/7 where k(n) is the 3-period sequence 1,-5,4,... reminiscent to A130815. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 30 2008]
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CROSSREFS
| Sequence in context: A107058 A101449 A134188 * A070529 A009145 A009292
Adjacent sequences: A140292 A140293 A140294 * A140296 A140297 A140298
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KEYWORD
| sign
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AUTHOR
| Paul Curtz (bpcrtz(AT)free.fr), May 25 2008
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EXTENSIONS
| More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 30 2008
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