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A123637
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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!*(n+1)!.
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1
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1, 4, 23, 238, 4285, 120056, 4807699, 259889218, 18207958073, 1603405689580, 173263178533711, 22534190356771094, 3471514311529290613, 625057269686305463008, 130043797443156653379275
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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EXAMPLE
| a(n) equals the sum of (2n+1) terms:
a(0) = 1;
a(1) = 1 + 1*1 + 1*1*2 = 4;
a(2) = 1 + 1*2 + 1*2*2 + 1*2*2*1 + 1*2*2*1*3 = 23;
a(3) = 1 + 1*3 + 1*3*2 + 1*3*2*2 + 1*3*2*2*3 + 1*3*2*2*3*1 + 1*3*2*2*3*1*4 = 238.
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PROG
| (PARI) {a(n)=sum(k=1, 2*n+1, prod(j=1, k, ((j+1)\2)*(j%2)+(n+1-(j\2))*((j-1)%2)))}
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CROSSREFS
| Cf. A123636.
Sequence in context: A188404 A105747 A099692 * A130890 A138578 A107765
Adjacent sequences: A123634 A123635 A123636 * A123638 A123639 A123640
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KEYWORD
| nonn
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AUTHOR
| Paul D. Hanna (pauldhanna(AT)juno.com), Oct 04 2006
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