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A123636
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a(n) = 1 + 1*n + 1*n*2 + 1*n*2*(n-1) + 1*n*2*(n-1)*3 + 1*n*2*(n-1)*3*(n-2) + ... + n!.
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1
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1, 1, 3, 10, 37, 176, 979, 6658, 50873, 451180, 4376911, 47740694, 560586613, 7248848608, 99837660875, 1492197903466, 23571796088689, 399706304138708, 7121101849585543, 135049981967575870, 2678257990821099821
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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EXAMPLE
| a(0) = a(1) = 1;
a(2) = 1 + 1*2 = 3;
a(3) = 1 + 1*3 + 1*3*2 = 10;
a(4) = 1 + 1*4 + 1*4*2 + 1*4*2*3 = 37;
a(5) = 1 + 1*5 + 1*5*2 + 1*5*2*4 + 1*5*2*4*3 = 176; ...
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PROG
| (PARI) {a(n)=if(n==0, 1, sum(k=1, n, prod(j=1, k, ((j+1)\2)*(j%2)+(n+1-(j\2))*((j-1)%2))))}
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CROSSREFS
| Cf. A123637.
Sequence in context: A064613 A138378 A005493 * A092816 A078109 A149045
Adjacent sequences: A123633 A123634 A123635 * A123637 A123638 A123639
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KEYWORD
| nonn
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AUTHOR
| Paul D. Hanna (pauldhanna(AT)juno.com), Oct 03 2006
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