login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A080170
Numbers k such that gcd(C(2*k,k), C(3*k,k), C(4*k,k), ..., C((k+1)*k,k) ) = 1.
2
29, 59, 69, 83, 89, 104, 119, 125, 131, 139, 153, 164, 167, 179, 181, 194, 197, 209, 219, 230, 233, 251, 259, 263, 272, 279, 285, 305, 307, 311, 314, 329, 335, 339, 356, 359, 363, 373, 379, 384, 389, 395, 398, 407, 417, 419, 428, 439, 441, 454, 455, 461
OFFSET
1,1
COMMENTS
a(n) = A051283(n) - 1 (conjectured). - Ralf Stephan, Feb 20 2004
MATHEMATICA
Select[Range[500], GCD@@Table[Binomial[k*#, # ], {k, 2, #+1}]==1&]
PROG
(Haskell)
a080170 n = a080170_list !! (n-1)
a080170_list = filter f [1..] where
f x = foldl1 gcd (map (flip a007318' x) [2*x, 3*x .. x*(x+1)]) == 1
-- Reinhard Zumkeller, May 30 2013
(PARI) isok(k) = gcd(vector(k, i, binomial(k+i*k, k))) == 1; \\ Jinyuan Wang, Feb 28 2020
CROSSREFS
Sequence in context: A004942 A033904 A184073 * A078848 A055784 A083821
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Jan 31 2003
STATUS
approved