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A232701 a(n) = (2*n-1)!! mod n!, where double factorial is A006882. 1
0, 1, 3, 9, 105, 315, 4095, 11025, 348705, 1545075, 17931375, 93087225, 3764185425, 45589819275, 1060569885375, 15877899662625, 900941666625, 5722531807867875, 90088576482279375, 1688777976676415625, 18148954872023600625, 320586579951629866875, 11054393914490520969375 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
(2n-1)!! is the product of first n odd numbers.
LINKS
EXAMPLE
a(4) = 1*3*5*7 mod (1*2*3*4) = 105 mod 24 = 9.
MATHEMATICA
o = 1; Reap[For[n = 1, n <= 99, n += 2, o *= n; m = Mod[o, (Quotient[n, 2] + 1)!]; Sow[m]]][[2, 1]] (* Jean-François Alcover, Oct 05 2017, translated from Alex Ratushnyak's Python code *)
PROG
(Python)
import math
o=1
for n in range(1, 99, 2):
o*=n
print str(o % math.factorial(n//2+1))+', ',
CROSSREFS
Cf. A006882, A232618, A024502 (floor((2*n-1)!! / n!)).
Sequence in context: A135989 A227772 A125652 * A364495 A340483 A018746
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Nov 28 2013
STATUS
approved

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Last modified June 23 23:43 EDT 2024. Contains 373661 sequences. (Running on oeis4.)