cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A228340 Triangle read by rows: T(n,k) = (n-1)*T(n-1,k) + T(n-2,k), with T(n,n-1)=1, T(n,n-2)=n-2, for n >= 1, 0 <= k <= n-1.

Original entry on oeis.org

1, 0, 1, 1, 1, 1, 3, 4, 2, 1, 13, 17, 9, 3, 1, 68, 89, 47, 16, 4, 1, 421, 551, 291, 99, 25, 5, 1, 3015, 3946, 2084, 709, 179, 36, 6, 1, 24541, 32119, 16963, 5771, 1457, 293, 49, 7, 1, 223884, 293017, 154751, 52648, 13292, 2673, 447, 64, 8, 1
Offset: 1

Views

Author

N. J. A. Sloane, Aug 29 2013

Keywords

Examples

			Triangle begins:
1,
0,1,
1,1,1,
3,4,2,1,
13,17,9,3,1,
68,89,47,16,4,1,
421,551,291,99,25,5,1,
3015,3946,2084,709,179,36,6,1,
...
		

Crossrefs

Diagonals give A058307, A058279, A228341. Row sums give A001040.

Programs

  • Haskell
    a228340 n k = a228340_tabl !! (n-1) !! k
    a228340_row n = a228340_tabl !! (n-1)
    a228340_tabl = map (reverse . fst) $ iterate f ([1], [1,0]) where
       f (us, vs'@( : vs@(v : ))) = (vs', ws) where
         ws = 1 : (v + 1) : zipWith (+) us (map (* (v + 2)) vs)
    -- Reinhard Zumkeller, Aug 31 2013
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