A199162 a(1) = 1, a(2) = 6; for n>2, a(n) = least number > a(n-1) which is a unique sum of two distinct earlier terms.

1, 6, 7, 8, 9, 10, 11, 12, 14, 24, 26, 27, 28, 29, 31, 45, 46, 47, 48, 49, 62, 68, 82, 83, 84, 85, 98, 104, 117, 122, 135, 142, 154, 155, 159, 172, 191, 192, 193, 194, 195, 209, 234, 245, 248, 249, 250, 265, 266, 267, 268, 270, 283, 302, 303, 304, 305, 306

Offset

1,2

Comments

An Ulam-type sequence - see A002858 for many further references, comments, etc.

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Ulam Sequence

Wikipedia, Ulam number

Index entries for Ulam numbers

Example

13 is not a term, as 13 = 7+6 = a(3)+a(2) and 13 = 12+1 = a(8)+a(1);
14 is a term, because 14 = 8 + 6 = a(4) + a(2) is unique for distinct terms, a(9) = 14.

Prog

(Haskell)
a199162 n = a199162_list !! (n-1)
a199162_list = 1 : 6 : ulam 2 6 a199162_list
-- Function ulam as defined in A002858.
-- Reinhard Zumkeller, Nov 03 2011

Crossrefs

Cf. A003663.

Sequence in context: A182307 A023384 A053407 * A120199 A162786 A269801

Adjacent sequences: A199159 A199160 A199161 * A199163 A199164 A199165

Keyword

nonn

Author

Reinhard Zumkeller, Nov 03 2011

Status

approved