A232863 Numbers k such that (2*k-1)!! mod k! is greater than (2k+1)!! mod (k+1)!.

16, 75, 82, 572, 5260, 33232, 99589, 200413, 2940392

Offset

1,1

Comments

Numbers k such that A232701(k) > A232701(k+1).

(2k-1)!! is the product of first k odd numbers.

Links

Table of n, a(n) for n=1..9.

Example

16 is in the sequence because A232701(16) > A232701(17).

Mathematica

o = 1; prev = cur = 0; Reap[For[n = 1, n < 3*10^6, n += 2, o *= n; prev = cur; cur = Mod[o, (Quotient[n, 2] + 1)!]; If[n > 1 && prev > cur, Print[(n - 1)/2]; Sow[(n - 1)/2]]]][[2, 1]] (* translated from Alex Ratushnyak's Python code *)

Prog

(Python)
o = f = 1
prev = 0
for n in range(1, 1000000):
  o *= 2*n-1
  f *= n
  cur = o % f
  if prev>cur:  print str(n-1)+', ',
  prev=cur
  if (n&8191)==0:  print '.',

Crossrefs

Cf. A000142, A006882, A232620, A232701.

Sequence in context: A124894 A126403 A197873 * A200786 A250353 A212690

Adjacent sequences: A232860 A232861 A232862 * A232864 A232865 A232866

Keyword

nonn,hard,more

Author

Alex Ratushnyak, Dec 01 2013

Status

approved