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A151626 Number of permutations of 2 indistinguishable copies of 1..n with exactly 4 adjacent element pairs in decreasing order. 2
0, 0, 1, 603, 47290, 1822014, 49258935, 1086859301, 21147576440, 379269758400, 6441229796061, 105398150289775, 1680774708581766, 26324724399068626, 407112461900381715, 6239897666881158537, 95036195852840662820, 1440959515956284422196, 21778829725476446172249 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..200

FORMULA

a(n) = 15^n - (2*n + 1)*10^n + binomial(2*n+1, 2)*6^n - binomial(2*n+1, 3)*3^n + binomial(2*n+1, 4). - Andrew Howroyd, May 07 2020

PROG

(PARI) a(n) = {15^n - (2*n + 1)*10^n + binomial(2*n+1, 2)*6^n - binomial(2*n+1, 3)*3^n + binomial(2*n+1, 4) } \\ Andrew Howroyd, May 07 2020

CROSSREFS

Column k=4 of A154283.

Sequence in context: A177685 A250907 A209550 * A031792 A020383 A234109

Adjacent sequences:  A151623 A151624 A151625 * A151627 A151628 A151629

KEYWORD

nonn

AUTHOR

R. H. Hardin, May 29 2009

EXTENSIONS

Terms a(12) and beyond from Andrew Howroyd, May 07 2020

STATUS

approved

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Last modified April 23 05:23 EDT 2021. Contains 343199 sequences. (Running on oeis4.)