OFFSET
1,1
COMMENTS
The set seems to have greater cardinality than its complement.
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000
EXAMPLE
7 is in the sequence as gcd(binomial(2*7, 7), 2*7 + 1) = gcd(3432, 15) = gcd(3*1144, 3*5) > 1. - David A. Corneth, Apr 03 2021
MATHEMATICA
Select[Range[200], GCD[Binomial[2 #, #], 2 #+1]>1&] (* Harvey P. Dale, May 11 2019 *)
PROG
(PARI) is(n) = { my(f = factor(2*n+1)); for(i = 1, #f~, if(val(2*n, f[i, 1])-2*val(n, f[i, 1]) > 0, return(1))); 0 }
val(n, p) = my(r=0); while(n, r+=n\=p); r \\ David A. Corneth, Apr 03 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Ralf Stephan, Dec 11 2004
STATUS
approved