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A056230
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.
9
1, 2, 3, 4, 6, 9, 7, 11, 17, 26, 12, 19, 30, 47, 73, 13, 25, 44, 74, 121, 194, 14, 27, 52, 96, 170, 291, 485, 15, 29, 56, 108, 204, 374, 665, 1150, 16, 31, 60, 116, 224, 428, 802, 1467, 2617, 18, 34, 65, 125, 241, 465, 893, 1695, 3162, 5779, 20, 38, 72, 137, 262
OFFSET
1,2
LINKS
EXAMPLE
Array begins
1 3 9 26 73 194 ...
.2 6 17 47 121 ...
. 4 11 30 74 ...
.. 7 19 44 ...
... 12 25 ...
.... 13 ...
PROG
(Haskell)
import Data.List (intersect, union, (\\))
a056230 n k = a056230_tabl !! (n-1) !! (k-1)
a056230_tabl = [1] : f [1] [2..] [1] where
f adiag (a:as) us | null (adiag' `intersect` us) =
adiag' : f adiag' (as \\ adiag') (us `union` adiag')
| otherwise = f adiag as us
where adiag' = scanl (+) a adiag
-- Reinhard Zumkeller, Nov 19 2011
CROSSREFS
Cf. A057153 (first row), A200379 (second row), A052474 (main diagonal), A057154 (numbers not used), A056231, A056232, A056233, A056234.
Sequence in context: A207831 A207826 A035312 * A285321 A253561 A354960
KEYWORD
nice,nonn,easy,tabl
AUTHOR
Jonas Wallgren, Jul 30, 2000.
STATUS
approved