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A063488 a(n) = (2*n-1)*(n^2 -n +2)/2. 21
1, 6, 20, 49, 99, 176, 286, 435, 629, 874, 1176, 1541, 1975, 2484, 3074, 3751, 4521, 5390, 6364, 7449, 8651, 9976, 11430, 13019, 14749, 16626, 18656, 20845, 23199, 25724, 28426, 31311, 34385, 37654, 41124, 44801, 48691, 52800, 57134 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Sum of two consecutive terms of A006003(n) = n*(n^2+1)/2. a(n) = A006003(n-1) + A006003(n). - Alexander Adamchuk, Jun 03 2006
If a 2-set Y and a 3-set Z are disjoint subsets of an n-set X then a(n-4) is the number of 5-subsets of X intersecting both Y and Z. - Milan Janjic, Sep 08 2007
LINKS
M. Janjic and B. Petkovic, A Counting Function, arXiv 1301.4550 [math.CO], 2013.
T. P. Martin, Shells of atoms, Phys. Rep., 273 (1996), 199-241, eq. (10).
FORMULA
G.f.: (1 + x)*(1 + x + x^2)/(1 - x)^4. - Jaume Oliver Lafont, Aug 30 2009
a(n) = A000217(A000217(n)) - A000217(A000217(n-2)). - Bruno Berselli, Oct 14 2016
E.g.f.: (-2 + 4*x + 3*x^2 + 2*x^3)*exp(x)/2 + 1. - G. C. Greubel, Dec 01 2017
MATHEMATICA
Table[(2 n - 1) (n^2 - n + 2)/2, {n, 1, 40}] (* Bruno Berselli, Oct 14 2016 *)
LinearRecurence[{4, -6, 4, -1}, {1, 6, 20, 49}, 50] (* G. C. Greubel, Dec 01 2017 *)
PROG
(PARI) { for (n=1, 1000, write("b063488.txt", n, " ", (2*n - 1)*(n^2 - n + 2)/2) ) } \\ Harry J. Smith, Aug 23 2009
(PARI) x='x+O('x^30); Vec(serlaplace((-2 + 4*x + 3*x^2 + 2*x^3)*exp(x)/2 + 1)) \\ G. C. Greubel, Dec 01 2017
(Magma) [(2*n-1)*(n^2 -n +2)/2: n in [1..30]]; // G. C. Greubel, Dec 01 2017
CROSSREFS
1/12*t*n*(2*n^2 - 3*n + 1) + 2*n - 1 for t = 2, 4, 6, ... gives A049480, A005894, A063488, A001845, A063489, A005898, A063490, A057813, A063491, A005902, A063492, A005917, A063493, A063494, A063495, A063496.
Partial sums of A005918.
Sequence in context: A331754 A050768 A161438 * A299292 A162209 A161699
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Aug 01 2001
STATUS
approved

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Last modified June 13 09:03 EDT 2024. Contains 373383 sequences. (Running on oeis4.)