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%I #10 May 20 2014 14:52:31
%S 1,2,3,4,6,9,7,11,17,26,12,19,30,47,73,13,25,44,74,121,194,14,27,52,
%T 96,170,291,485,15,29,56,108,204,374,665,1150,16,31,60,116,224,428,
%U 802,1467,2617,18,34,65,125,241,465,893,1695,3162,5779,20,38,72,137,262
%N Construct difference array so that (1) first row begins with 1, (2) every row is monotonic increasing, (3) no number appears more than once, (4) smallest number not yet used begins a new row. Sequence gives array read by antidiagonals.
%H Reinhard Zumkeller, <a href="/A056230/b056230.txt">Antidiagonals n=1..150 of array, flattened</a>
%e Array begins
%e 1 3 9 26 73 194 ...
%e .2 6 17 47 121 ...
%e . 4 11 30 74 ...
%e .. 7 19 44 ...
%e ... 12 25 ...
%e .... 13 ...
%o (Haskell)
%o import Data.List (intersect, union, (\\))
%o a056230 n k = a056230_tabl !! (n-1) !! (k-1)
%o a056230_tabl = [1] : f [1] [2..] [1] where
%o f adiag (a:as) us | null (adiag' `intersect` us) =
%o adiag' : f adiag' (as \\ adiag') (us `union` adiag')
%o | otherwise = f adiag as us
%o where adiag' = scanl (+) a adiag
%o -- _Reinhard Zumkeller_, Nov 19 2011
%Y Cf. A057153 (first row), A200379 (second row), A052474 (main diagonal), A057154 (numbers not used), A056231, A056232, A056233, A056234.
%K nice,nonn,easy,tabl
%O 1,2
%A _Jonas Wallgren_, Jul 30, 2000.
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