A128287 Nonprime numbers k such that k divides A014137(k).

1, 8, 133, 49378

Offset

1,2

Comments

Prime p divides A014137(p) for p in A045309 (primes congruent to {0, 2} mod 3).

a(5) > 5000000. - Chai Wah Wu, Nov 13 2014

Links

Table of n, a(n) for n=1..4.

Example

1 is nonprime and divides A014137(1) = 2, so 1 is a term.
8 is nonprime and divides A014137(8) = 2056, so 8 is a term.

Mathematica

s = 1; Do[s = s + (2n)!/n!/(n+1)!; If[ !PrimeQ[n] && Mod[s, n] == 0, Print[n]], {n, 1000}]

Prog

(Python)
from __future__ import division
from sympy import isprime
A128287_list, x, s = [1], 1, 2
for i in range(2, 10**5):
....x = x*(4*i-2)//(i+1)
....s += x
....if not (isprime(i) or s % i):
........A128287_list.append(i) # Chai Wah Wu, Nov 13 2014

Crossrefs

Cf. A014137, A000108, A045309, A045309.

Sequence in context: A237026 A079912 A281948 * A221545 A316177 A003375

Adjacent sequences: A128284 A128285 A128286 * A128288 A128289 A128290

Keyword

bref,hard,more,nonn

Author

Alexander Adamchuk, Feb 23 2007

Extensions

One more term from Ryan Propper, Apr 02 2007

Status

approved