OFFSET
1,1
COMMENTS
It seems there is a typo in the Gua and Zeng link, it gives 175 instead of 185 as a term.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..10000
Victor J.W. Guo and Jiang Zeng, Factors of binomial sums from the Catalan triangle, Journal of Number Theory 130 (2010) 172-186.
MATHEMATICA
Select[Range[2, 1100], !PrimePowerQ[#]&&GCD[Binomial[2#-1, #], #]==1&] (* Harvey P. Dale, May 26 2020 *)
PROG
(PARI) isok(n) = (n != 1) && !isprimepower(n) && (gcd(binomial(2*n-1, n), n) == 1);
(Magma) [n : n in [2..2000] | not IsPrimePower(n) and Gcd(Binomial(2*n-1, n), n) eq 1]; // Vincenzo Librandi, Jan 26 2016
(Python)
from __future__ import division
from fractions import gcd
from sympy import factorint
A268083_list, b = [], 1
for n in range(1, 10**4):
if len(factorint(n)) > 1 and gcd(b, n) == 1:
A268083_list.append(n)
b = b*2*(2*n+1)//(n+1) # Chai Wah Wu, Jan 26 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Jan 26 2016
STATUS
approved