OFFSET
1,1
COMMENTS
Each positive integer n has a unique binomial expansion n = C(n_t,t) + C(n_{t-1},t-1) + ... + C(n_v,v) for a given order t, where n_t > n_{t-1} > ... > n_v >= v >= 1. The sequence contains those n for which v=1 and n_v=1 at t=3. The equivalent sequence for t=2 is A000124.
EXAMPLE
Expansions in t=3 for n=19 up to 23 are n=19=C(5,3)+C(4,2)+C(3,1);
n=20=C(6,3); n=21=C(6,3)+C(2,2); n=22=C(6,3)+C(2,2)+C(1,1); n=23=C(6,3)+C(3,2).
Of these, only n=22 has a C(1,1) component and makes it into the sequence.
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
R. J. Mathar, Mar 15 2007
STATUS
approved