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Search: id:A001250
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| A001250 |
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Expansion of 2*(tan x + sec x); also of (tan x + sec x)^2.
(Formerly M1235 N0472)
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+0
6
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| 1, 2, 4, 10, 32, 122, 544, 2770, 15872, 101042, 707584, 5405530, 44736512, 398721962, 3807514624, 38783024290, 419730685952, 4809759350882, 58177770225664, 740742376475050, 9902996106248192, 138697748786275802
(list; graph; listen)
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OFFSET
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0,2
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 261.
F. N. David, M. G. Kendall and D. E. Barton, Symmetric Function and Allied Tables, Cambridge, 1966, p. 262.
C. Davis, Problem 4755, Amer. Math. Monthly, 65 (1958), 533-534.
S. Kitaev, Multi-avoidance of generalized patterns, Discrete Math., 260 (2003), 89-100. (See p. 100.)
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LINKS
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Eric Weisstein's World of Mathematics, Alternating Permutation
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PROGRAM
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(PARI) a(n)=local(v=[1], t); if(n<0, 0, for(k=2, n+3, t=0; v=vector(k, i, if(i>1, t+=v[k+1-i]))); v[3]) (from Michael Somos)
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CROSSREFS
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Apart from initial term, twice A000111. A diagonal of A010094.
Sequence in context: A071954 A120017 A000736 this_sequence A013032 A098830 A121277
Adjacent sequences: A001247 A001248 A001249 this_sequence A001251 A001252 A001253
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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