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A060823
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4-wave sequence beginning with 2's with middles dropped.
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1
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2, 2, 8, 20, 60, 170, 492, 1414, 4074, 11728, 33772, 97240, 279994, 806208, 2321386, 6684162, 19246280, 55417452, 159568196, 459458306, 1322957468, 3809304206, 10968454314, 31582405472, 90937912212, 261845282320, 753953441490
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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LINKS
| Harry J. Smith, Table of n, a(n) for n=2,...,200
F. v. Lamoen, Wave sequences
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FORMULA
| a(n)=2*a(n-1)+3*a(n-2)-a(n-3)-a(n-4) - Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Mar 22 2003
G.f.: -2*x^2*(-1+x+x^2)/((1+x)*(x^3-3*x+1)). a(n)=2*A006357(n-3). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 15 2009]
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PROG
| (PARI) { for (n=2, 200, if (n>5, a=2*a1 + 3*a2 - a3 - a4; a4=a3; a3=a2; a2=a1; a1=a, if (n==2, a=a4=2, if (n==3, a=a3=2, if (n==4, a=a2=8, a=a1=20)))); write("b060823.txt", n, " ", a); ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Jul 12 2009]
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CROSSREFS
| Cf. A038197.
Sequence in context: A067640 A098277 A080040 * A178076 A137774 A167532
Adjacent sequences: A060820 A060821 A060822 * A060824 A060825 A060826
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KEYWORD
| easy,nonn
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AUTHOR
| Jason Earls (zevi_35711(AT)yahoo.com), May 01 2001
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EXTENSIONS
| More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Mar 22 2003
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