OFFSET
1,1
COMMENTS
Complement of A003714. It appears that n is in the sequence if and only if C(3n,n) is even. - Benoit Cloitre, Mar 09 2003
Since the binary representation of these numbers contains two adjacent 1's, so for these values of n, we will have (n XOR 2n XOR 3n) != 0, and thus a two player Nim game with three heaps of (n, 2n, 3n) stones will be a winning configuration for the first player. - V. Raman, Sep 17 2012
A048728(a(n)) > 0. - Reinhard Zumkeller, May 13 2014
The set of numbers x such that Or(x,3*x) <> 3*x. - Gary Detlefs, Jun 04 2024
LINKS
FORMULA
a(n) ~ n. - Charles R Greathouse IV, Sep 19 2012
MAPLE
q:= n-> verify([1$2], Bits[Split](n), 'sublist'):
select(q, [$0..200])[]; # Alois P. Heinz, Oct 22 2021
PROG
(PARI) is(n)=bitand(n, n+n)>0 \\ Charles R Greathouse IV, Sep 19 2012
(Haskell)
a004780 n = a004780_list !! (n-1)
a004780_list = filter ((> 1) . a048728) [1..]
-- Reinhard Zumkeller, May 13 2014
(Python)
from itertools import count, islice
def A004780_gen(startvalue=1): # generator of terms >= startvalue
return filter(lambda n:n&(n<<1), count(max(startvalue, 1)))
CROSSREFS
KEYWORD
nonn,easy,base
AUTHOR
EXTENSIONS
Offset corrected by Reinhard Zumkeller, Jul 28 2010
STATUS
approved