login
This site is supported by donations to The OEIS Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A227415 a(n) = (n+1)!! mod n!!. 1
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 (list; graph; refs; listen; history; text; internal format)
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: A256614 A021369 A242304 * A298042 A051430 A185510

Adjacent sequences:  A227412 A227413 A227414 * A227416 A227417 A227418

KEYWORD

nonn,easy

AUTHOR

Alex Ratushnyak, Jul 10 2013

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 17 14:12 EST 2019. Contains 319225 sequences. (Running on oeis4.)