A227415 a(n) = (n+1)!! mod n!!.

0, 0, 1, 2, 7, 3, 9, 69, 177, 60, 2715, 4500, 42975, 104580, 91665, 186795, 3493665, 13497435, 97345395, 442245825, 2601636975, 13003053525, 70985324025, 64585694250, 57891366225, 3576632909850, 9411029102475, 147580842959550, 476966861546175, 5708173568847750

Offset

0,4

Comments

a(n) is divisible by A095987(n+1), and is nonzero for n > 1. - Robert Israel, Mar 10 2016

Links

Robert Israel, Table of n, a(n) for n = 0..800

Formula

a(n) = A006882(n+1) mod A006882(n).

Example

a(4) = 5*3 mod 4*2 = 15 mod 8 = 7.

Maple

seq(doublefactorial(n+1) mod doublefactorial(n), n=0..100); # Robert Israel, Mar 10 2016

Prog

(Python)
for n in range(2, 77):
    prOdd = prEven = 1
    for i in range(1, n, 2): prOdd *= i
    for i in range(2, n, 2): prEven *= i
    if n&1: print str(prEven % prOdd)+', ',
    else:   print str(prOdd % prEven)+', ',

Crossrefs

Cf. A006882, A095987.

Cf. A007911: (n-1)!! - (n-2)!!

Cf. A007912: (n-1)!! - (n-2)!! (mod n).

Cf. A060696: (n-1)!! + (n-2)!! except first two terms.

Sequence in context: A021369 A340711 A242304 * A361207 A309156 A298042

Adjacent sequences: A227412 A227413 A227414 * A227416 A227417 A227418

Keyword

nonn,easy

Author

Alex Ratushnyak, Jul 10 2013

Status

approved