A081026 Variation on Ulam numbers: a(1) = 1; a(2) = 2; for n>2, a(n) = smallest (n odd) or largest (n even) number > a(n-1) that is a unique sum of two distinct earlier terms.

1, 2, 3, 5, 6, 11, 12, 23, 24, 47, 48, 95, 96, 191, 192, 383, 384, 767, 768, 1535, 1536, 3071, 3072, 6143, 6144, 12287, 12288, 24575, 24576, 49151, 49152, 98303, 98304, 196607, 196608, 393215, 393216, 786431, 786432, 1572863, 1572864, 3145727

Offset: 1

Author

David W. Wilson, Mar 02 2003

Keywords

• nonn

References

• Dan Asimov, post to math-fun mailing list, Feb 11, 2003.

Crossrefs

Cf. A002858, A081025.

Formula

Appears that a(2k) = 3*2^(k-1)-1, a(2k+1) = 3*2^(k-1) for k >= 1.