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A244865 Number of 3 X 3 symmetric matrices with row and column sums <= n. 2
1, 14, 85, 336, 1023, 2610, 5860, 11942, 22555, 40068, 67677, 109578, 171157, 259196, 382096, 550116, 775629, 1073394, 1460845, 1958396, 2589763, 3382302, 4367364, 5580666, 7062679, 8859032, 11020933, 13605606, 16676745, 20304984, 24568384, 29552936, 35353081, 42072246, 49823397, 58729608 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
LINKS
R. P. Stanley, Examples of Magic Labelings, Unpublished Notes, 1973 [Cached copy, with permission]
FORMULA
G.f.: (1 + 8*x + 15*x^2 + 8*x^3 + x^4) / ((1 - x)^7*(1 + x)).
From Colin Barker, Jan 11 2017: (Start)
a(n) = (15*(127+(-1)^n) + 6432*n + 8936*n^2 + 6480*n^3 + 2570*n^4 + 528*n^5 + 44*n^6) / 1920.
a(n) = 6*a(n-1) - 14*a(n-2) + 14*a(n-3) - 14*a(n-5) + 14*a(n-6) - 6*a(n-7) + a(n-8) for n>7.
(End)
PROG
(PARI) Vec((1 + 8*x + 15*x^2 + 8*x^3 + x^4) / ((1 - x)^7*(1 + x)) + O(x^40)) \\ Colin Barker, Jan 11 2017
CROSSREFS
Sequence in context: A341854 A025607 A272103 * A059600 A206621 A372148
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jul 07 2014
STATUS
approved

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Last modified June 21 14:19 EDT 2024. Contains 373547 sequences. (Running on oeis4.)