A199162 - OEIS

%I #8 Jul 13 2013 12:04:18

%S 1,6,7,8,9,10,11,12,14,24,26,27,28,29,31,45,46,47,48,49,62,68,82,83,

%T 84,85,98,104,117,122,135,142,154,155,159,172,191,192,193,194,195,209,

%U 234,245,248,249,250,265,266,267,268,270,283,302,303,304,305,306

%N 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.

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

%H Reinhard Zumkeller, <a href="/A199162/b199162.txt">Table of n, a(n) for n = 1..10000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/UlamSequence.html">Ulam Sequence</a>

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Ulam_number">Ulam number</a>

%H <a href="/index/U#Ulam_num">Index entries for Ulam numbers</a>

%e 13 is not a term, as 13 = 7+6 = a(3)+a(2) and 13 = 12+1 = a(8)+a(1);

%e 14 is a term, because 14 = 8 + 6 = a(4) + a(2) is unique for distinct terms, a(9) = 14.

%o (Haskell)

%o a199162 n = a199162_list !! (n-1)

%o a199162_list = 1 : 6 : ulam 2 6 a199162_list

%o -- Function ulam as defined in A002858.

%o -- _Reinhard Zumkeller_, Nov 03 2011

%Y Cf. A003663.

%K nonn

%O 1,2

%A _Reinhard Zumkeller_, Nov 03 2011