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 A123346 Mirror image of the Bell triangle A011971, which is also called the Pierce triangle or Aitken's array. 4
 1, 2, 1, 5, 3, 2, 15, 10, 7, 5, 52, 37, 27, 20, 15, 203, 151, 114, 87, 67, 52, 877, 674, 523, 409, 322, 255, 203, 4140, 3263, 2589, 2066, 1657, 1335, 1080, 877, 21147, 17007, 13744, 11155, 9089, 7432, 6097, 5017, 4140, 115975, 94828, 77821, 64077, 52922, 43833, 36401, 30304, 25287, 21147 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS a(n,k) is k-th difference of Bell numbers, with a(n,1) = A000110(n) for  n>0, a(n,k) = a(n,k-1) - a(n-1, k-1), k<=n, with diagonal (k=n) also equal to Bell numbers (n>=0). - Richard R. Forberg, Jul 13 2013 From Don Knuth, Jan 29 2018: (Start) If the offset here is changed from 0 to 1, then we can say: a(n,k) is the number of equivalence classes of [n] in which 1 not equiv to 2, ..., 1 not equiv to k. In Volume 4A, page 418, I pointed out that a(n,k) is the number of set partitions in which k is the smallest of its block. And in exercise 7.2.1.5--33, I pointed out that a(n,k) is the number of equivalence relations in which 1 not equiv to 2, 2 not equiv to 3, ..., k-1 not equiv to k. (End) REFERENCES D. E. Knuth, The Art of Computer Programming, vol. 4A, Combinatorial Algorithms, Section 7.2.1.5 (p. 418). LINKS Reinhard Zumkeller, Rows n = 0..100 of triangle, flattened A. Dil, Veli Kurt, Investigating Geometric and Exponential Polynomials with Euler-Seidel Matrices, J. Int. Seq. 14 (2011) # 11.4.6 Don Knuth, Email to N. J. A. Sloane, Jan 29 2018 Eric Weisstein's World of Mathematics, Bell Triangle. FORMULA a(n,k) = Sum_{i=k..n} binomial(n-k,i-k)*Bell(i). - Vladeta Jovovic, Oct 14 2006 EXAMPLE Triangle begins: 1 2 1 5 3 2 15 10 7 5 52 37 27 20 15 203 151 114 87 67 52 MATHEMATICA a[n_, k_] := Sum[Binomial[n - k, i - k] BellB[i], {i, k, n}]; Table[a[n, k], {n, 0, 9}, {k, 0, n}] // Flatten (* Jean-François Alcover, Aug 03 2018 *) PROG (Haskell) a123346 n k = a123346_tabl !! n !! k a123346_row n = a123346_tabl !! n a123346_tabl = map reverse a011971_tabl -- Reinhard Zumkeller, Dec 09 2012 (Python) # requires python 3.2 or higher. Otherwise use def'n of accumulate in python docs. from itertools import accumulate A123346_list = blist = [1] for _ in range(2*10**2): ....b = blist[-1] ....blist = list(accumulate([b]+blist)) ....A123346_list += reversed(blist) # Chai Wah Wu, Sep 02 2014, updated Chai Wah Wu, Sep 20 2014 CROSSREFS Cf. A011971. Borders give Bell numbers A000110. Diagonals give A005493, A011965, A011966, A011968, A011969, A046934, A011972, A094577, A095149, A106436, A108041, A108042, A108043. Sequence in context: A287548 A067323 A106534 * A163840 A122833 A193692 Adjacent sequences:  A123343 A123344 A123345 * A123347 A123348 A123349 KEYWORD nonn,tabl AUTHOR N. J. A. Sloane, Oct 14 2006 EXTENSIONS More terms from Alexander Adamchuk and Vladeta Jovovic, Oct 14 2006 STATUS approved

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Last modified July 23 19:00 EDT 2021. Contains 346259 sequences. (Running on oeis4.)