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A007607
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Skip 1, take 2, skip 3, etc.
(Formerly M0821)
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5
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2, 3, 7, 8, 9, 10, 16, 17, 18, 19, 20, 21, 29, 30, 31, 32, 33, 34, 35, 36, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| a(A000290(n)) = A001105(n). [Reinhard Zumkeller, Feb 12 2011]
A057211(a(n)) = 0. [Reinhard Zumkeller, Dec 30 2011]
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REFERENCES
| R. Honsberger, Mathematical Gems III, M.A.A., 1985, p. 177.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
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FORMULA
| G.f.: 1/(1-x) * [1/(1-x) + x*sum{k>=1, (2k+1)x^(k(k+1))}]. - Ralf Stephan, Mar 03 2004
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MATHEMATICA
| Flatten[ Table[i, {j, 2, 16, 2}, {i, j(j - 1)/2 + 1, j(j + 1)/2}]] (from Robert G. Wilson v Mar 11 2004)
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PROG
| (Haskell)
a007607 n = a007607_list !! (n-1)
a007607_list = skipTake 1 [1..] where
skipTake k xs = take (k + 1) (drop k xs)
++ skipTake (k + 2) (drop (2*k + 1) xs)
-- Reinhard Zumkeller, Feb 12 2011
(PARI) for(m=0, 10, for(n=2*m^2+3*m+2, 2*m^2+5*m+3, print1(n", "))) \\ Charles R Greathouse IV, Feb 12 2011
(Haskell)
a007607_list' = f $ tail $ scanl (+) 0 [1..] where
f (t:t':t'':ts) = [t+1..t'] ++ f (t'':ts)
-- Reinhard Zumkeller, Feb 12 2011
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CROSSREFS
| Cf. A063656, A004202, A063657, A007606, A064801, A004202.
Complement of A007606.
Sequence in context: A154432 A047361 A037461 * A076682 A194381 A047245
Adjacent sequences: A007604 A007605 A007606 * A007608 A007609 A007610
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Robert G. Wilson v (rgwv(AT)rgwv.com), Mira Bernstein (mira(AT)math.berkeley.edu)
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