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

1,2

References

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

Links

Table of n, a(n) for n=1..42.

Formula

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

Crossrefs

Cf. A002858, A081025.

Sequence in context: A127524 A117086 A344551 * A137808 A275525 A091909

Adjacent sequences: A081023 A081024 A081025 * A081027 A081028 A081029

Keyword

nonn

Author

David W. Wilson, Mar 02 2003

Status

approved