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A138163
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Number of permutations of {1,2,...,n} containing exactly 5 occurrences of the pattern 132.
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3
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5, 55, 394, 2225, 11539, 57064, 273612, 1283621, 5924924, 27005978, 121861262, 545368160, 2423923480, 10710273856, 47085144255, 206085075295, 898489543020, 3903621095130, 16906888008960, 73018012573950, 314540265217362
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OFFSET
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5,1
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REFERENCES
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B. K. Nakamura, Computational methods in permutation patterns, PhD Dissertation, Rutgers University, May 2013.
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LINKS
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FORMULA
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a(n) = (n^12+170n^11+1861n^10-88090n^9-307617n^8+27882510n^7 -348117457n^6 +2119611370n^5 -6970280884n^4 +10530947320n^3 +2614396896n^2 -30327454080n +29059430400)(2n-15)!/[120 n!(n-7)! ] for n>=8; a(5)=5; a(6)=55; a(7)=394.
G.f.: (1/2)[P(x) + Q(x)/(1-4x)^(9/2)], where P(x) = 14x^5 - 17x^4 + x^3 - 16x^2 + 14x - 2, Q(x)= -50x^11 - 2568x^10 - 10826x^9 + 16252x^8 - 12466x^7 + 16184x^6 - 16480x^5 + 9191x^4 - 2893x^3 + 520x^2 - 50x + 2.
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EXAMPLE
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a(5)=5 because we have 13542, 14532, 15243, 15342 and 15423.
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MAPLE
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a:=proc(n) options operator, arrow: (1/120)*(n^12+170*n^11 +1861*n^10 -88090*n^9 -307617*n^8 +27882510*n^7 -348117457*n^6 +2119611370*n^5 -6970280884*n^4 +10530947320*n^3 +2614396896*n^2 -30327454080*n +29059430400) *factorial(2*n-15) / (factorial(n)*factorial(n-7)) end proc: 5, 55, 394, seq(a(n), n = 8 .. 25);
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MATHEMATICA
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terms = 21; offset = 5;
P[x_] := 14 x^5 - 17 x^4 + x^3 - 16 x^2 + 14 x - 2;
Q[x_] := -50 x^11 - 2568 x^10 - 10826 x^9 + 16252 x^8 - 12466 x^7 + 16184 x^6 - 16480 x^5 + 9191 x^4 - 2893 x^3 + 520 x^2 - 50 x + 2;
Drop[CoefficientList[(1/2) (P[x] + Q[x]/(1 - 4 x)^(9/2)) + O[x]^(terms + offset), x], offset] (* Jean-François Alcover, Dec 13 2017 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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