%I #10 Oct 30 2018 10:31:02

%S 5,24,29,42,72,90,93,112,120,125,138,158,172,175,192,197,200,205,208,

%T 213,218,230,235,264,282,285,302,305,310,321,324,329,333,364,372,375,

%U 378,386,416,430,439,452,455,477,496,504,509,522,542,556

%N Form an array with 3 rows: row 1 begins with 1; all rows are increasing; each entry is sum of 2 entries above it; each number appears at most once; smallest unused number is appended to first row if possible. Sequence gives numbers not used.

%H Zak Seidov and Reinhard Zumkeller, <a href="/A056234/b056234.txt">Table of n, a(n) for n = 1..10000</a>

%e Array begins

%e 1 2 4 7 8 10 12 ...

%e .3 6 11 15 18 ...

%e . 9 17 26 33 ...

%o (Haskell)

%o a056234 n = a056234_list !! (n-1)

%o a056234_list = notUsed 1 a056231_list a056232_list a056233_list where

%o notUsed x us'@(u:us) vs'@(v:vs) ws'@(w:ws)

%o | x == u = notUsed (x + 1) us vs' ws'

%o | x == v = notUsed (x + 1) us' vs ws'

%o | x == w = notUsed (x + 1) us' vs' ws

%o | otherwise = x : notUsed (x + 1) us' vs' ws'

%o -- _Reinhard Zumkeller_, Nov 07 2011

%Y Cf. A056231, A056232, A056233. See also A057153, A052474, A057154, A056230.

%K nonn,nice,easy

%O 1,1

%A _N. J. A. Sloane_, E. M. Rains, Aug 22 2000