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A052992
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Expansion of 1/((1-x)(1-2x)(1+2x)).
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2
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1, 1, 5, 5, 21, 21, 85, 85, 341, 341, 1365, 1365, 5461, 5461, 21845, 21845, 87381, 87381, 349525, 349525, 1398101, 1398101, 5592405, 5592405, 22369621, 22369621, 89478485, 89478485, 357913941, 357913941, 1431655765, 1431655765
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| a(n)=sum of square divisors of 2^n. - Paul Barry (pbarry(AT)wit.ie), Oct 13 2005
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 1068
Index to sequences with linear recurrences with constant coefficients, signature (1,4,-4).
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FORMULA
| G.f.: 1/(-1+4*x^2)/(-1+x)
Recurrence: {a(1)=1, a(0)=1, -4*a(n)-1+a(n+2)=0}
-1/3+Sum(1/6*(1+4*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+4*_Z^2))
a(n)=sum{k=0..n, 2^k(1+(-1)^k)/2} - Paul Barry (pbarry(AT)wit.ie), Nov 24 2003
a(n)= a(n-1) + 4*a(n-2) - 4*a(n-3). - Paul Curtz, Apr 27 2011
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MAPLE
| spec := [S, {S=Prod(Sequence(Prod(Union(Z, Z), Union(Z, Z))), Sequence(Z))}, unlabeled ]: seq(combstruct[count ](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A171219 A146043 A116400 * A147254 A007028 A097336
Adjacent sequences: A052989 A052990 A052991 * A052993 A052994 A052995
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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EXTENSIONS
| More terms from James A. Sellers (sellersj(AT)math.psu.edu), Jun 08 2000
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