1,3

The first two are zero because the Ulam sequence (A002858) is initialized for those terms. The smaller term in the sum is in A080328 and the indices are in A080330 and A080331.

T. D. Noe, Table of n, a(n) for n=1..10000

The 11th Ulam number (26) is the sum of the 6th Ulam number (8) and the 10th Ulam number (18), so a(11)=18.

Cf. A002858, A080328, A080330, A080331.

Sequence in context: A018362 A033056 A060469 * A002858 A211522 A105799

Adjacent sequences: A080326 A080327 A080328 * A080330 A080331 A080332

nonn

Jud McCranie, Feb 15 2003

approved