A113550 - OEIS

A113550

a(n) = product of n successive numbers up to n, if n is odd a(n) = n*(n-1)*.. = n!,if n is even a(n) = n(n+1)(n+2)... 'n' terms.

1, 6, 6, 840, 120, 332640, 5040, 259459200, 362880, 335221286400, 39916800, 647647525324800, 6227020800, 1748648318376960000, 1307674368000, 6288139352883548160000, 355687428096000, 29051203810321992499200000

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OFFSET

1,2

COMMENTS

a(2n-1)*a(2n) = (4n-1)!. a(1)*a(2) = 3!, a(3)*a(4) = 7!.

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..350

FORMULA

a(1) = 1, a(2n-1) = (2n-1)!, a(2n) = (4n-1)!/(2n-1)!.

EXAMPLE

a(3) = 3*2*1 = 6, a(4)= 4*5*6*7=840.

MATHEMATICA

n = 1; anfunc[n_] := (If [EvenQ[n], {an = n, Do[an = an*(n + i), {i, n - 1}]}, an = n! ]; an) Table[anfunc[n], {n, 1, 30}] - Elizabeth A. Blickley (Elizabeth.Blickley(AT)gmail.com), Mar 10 2006

CROSSREFS

Cf. A113549.

Sequence in context: A213149 A267727 A268144 * A370738 A221400 A330157

Adjacent sequences: A113547 A113548 A113549 * A113551 A113552 A113553

KEYWORD

easy,nonn

AUTHOR

Amarnath Murthy, Nov 03 2005

EXTENSIONS

More terms from Elizabeth A. Blickley (Elizabeth.Blickley(AT)gmail.com), Mar 10 2006

STATUS

approved