A128287 - OEIS

A128287

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

1, 8, 133, 49378

(list; graph; refs; listen; history; text; internal format)

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

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

KEYWORD

bref,hard,more,nonn

AUTHOR

EXTENSIONS

One more term from Ryan Propper, Apr 02 2007

STATUS

approved