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A151656 Number of permutations of 7 indistinguishable copies of 1..n with exactly 2 adjacent element pairs in decreasing order. 2
0, 441, 35623, 1561238, 59287158, 2165511047, 78259307721, 2820153607740, 101551366735840, 3656082204395957, 131621033827371963, 4738375497166097906, 170581677602043334746, 6140941779058210902771, 221073915991189916489149, 7958661078139728516094136 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
Index entries for linear recurrences with constant coefficients, signature (55,-799,4381,-8884,7552,-2304).
FORMULA
a(n) = 36^n - (7*n + 1)*8^n + 7*n*(7*n + 1)/2. - Andrew Howroyd, May 06 2020
From Colin Barker, Jul 18 2020: (Start)
G.f.: 49*x^2*(9 + 232*x - 932*x^2 - 1024*x^3) / ((1 - x)^3*(1 - 8*x)^2*(1 - 36*x)).
a(n) = 55*a(n-1) - 799*a(n-2) + 4381*a(n-3) - 8884*a(n-4) + 7552*a(n-5) - 2304*a(n-6) for n>6.
(End)
PROG
(PARI) a(n) = {36^n - (7*n + 1)*8^n + 7*n*(7*n + 1)/2} \\ Andrew Howroyd, May 06 2020
(PARI) concat(0, Vec(49*x^2*(9 + 232*x - 932*x^2 - 1024*x^3) / ((1 - x)^3*(1 - 8*x)^2*(1 - 36*x)) + O(x^40))) \\ Colin Barker, Jul 18 2020
CROSSREFS
Cf. A151624.
Sequence in context: A221248 A220680 A189278 * A264088 A264277 A268874
KEYWORD
nonn,easy
AUTHOR
R. H. Hardin, May 29 2009
EXTENSIONS
Terms a(7) and beyond from Andrew Howroyd, May 06 2020
STATUS
approved

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Last modified July 19 04:24 EDT 2024. Contains 374388 sequences. (Running on oeis4.)