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A135370
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a(1)=1; then if n even a(n)=n+a(n-1), if n odd a(n)=2*n+a(n-1).
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5
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1, 3, 9, 13, 23, 29, 43, 51, 69, 79, 101, 113, 139, 153, 183, 199, 233, 251, 289, 309, 351, 373, 419, 443, 493, 519, 573, 601, 659, 689, 751, 783, 849, 883, 953, 989, 1063, 1101, 1179, 1219, 1301, 1343, 1429, 1473, 1563, 1609, 1703, 1751, 1849
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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LINKS
| Pierre CAMI, Table of n, a(n) for n = 1..1000
Index to sequences with linear recurrences with constant coefficients, signature (1,2,-2,-1,1).
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FORMULA
| a(n) ~ 0.75*n^2 (the sequence a(n)/n^2 has limit 3/4). - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Dec 10 2007
G.f.: x*(1+2*x+4*x^2-x^4)/((1+x)^2*(1-x)^3)). a(n) = a(n-1) +2*a(n-2) -2*a(n-3) -a(n-4) +a(n-5) = -7/8 +3*n*(n+1)/4 -(-1)^n*(1+2*n)/8. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 24 2008]
a(n)=(lcm(f(n),f(n)+3)-1)/3, where f(n)=floor((3*n-1)/2). [From Gary Detlefs,(gdetlefs(AT)aol.com), May 14 2011]
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MATHEMATICA
| a = {1}; For[n = 2, n < 100, n++, If[OddQ[n], AppendTo[a, 2*n + a[[ -1]]], AppendTo[a, n + a[[ -1]]]]]; a - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Dec 10 2007
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PROG
| (PARI) a(n)=lcm((3*n-1)\2, (3*n+5)\2)\3 \\ Charles R Greathouse IV, Dec 28 2011
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CROSSREFS
| Cf. A001651.
Sequence in context: A197569 A118570 A004617 * A206802 A022408 A126827
Adjacent sequences: A135367 A135368 A135369 * A135371 A135372 A135373
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KEYWORD
| nonn,easy
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AUTHOR
| Pierre CAMI (pierre-cami(AT)bbox.fr), Dec 09 2007
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EXTENSIONS
| More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Dec 10 2007
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