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 A121868 Let A(0) = 1, B(0) = 0; A(n+1) = Sum_{k=0..n} binomial(n,k)*B(k), B(n+1) = Sum_{k=0..n} -binomial(n,k)*A(k); entry gives B sequence (cf. A121867). 13
 0, -1, -1, 0, 5, 23, 74, 161, -57, -3466, -27361, -155397, -687688, -1888525, 4974059, 134695952, 1400820897, 11055147275, 70658948426, 327448854237, 223871274083, -19116044475298, -314203665206509, -3562429698724513, -33024521386113840, -250403183401213513 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS Stirling transform of (I^(n+1)+(-I)^(n+1))/2 = (0,-1,0,1,..) repeated. LINKS Alois P. Heinz, Table of n, a(n) for n = 0..250 A. Fekete and G. Martin, Problem 10791: Squared Series Yielding Integers, Amer. Math. Monthly, 108 (No. 2, 2001), 177-178. V. V. Kruchinin, Composition of ordinary generating functions, arXiv:1009.2565 [math.CO], 2010. FORMULA This sequence and its companion A121867 are related to the pair of constants cos(1) + sin(1) and cos(1) - sin(1) and may be viewed as generalizations of the Uppuluri-Carpenter numbers (complementary Bell numbers) A000587. Define E_2(k) = Sum_{n >= 0} (-1)^floor(n/2) *n^k/n! for k = 0,1,2,... . Then E_2(0) = cos(1) + sin(1) and E_2(1) = cos(1) - sin(1). Furthermore, E_2(k) is an integral linear combination of E_2(0) and E_2(1) (a Dobinski-type relation). For example, E_2(2) = - E_2(0) + E_2(1), E_2(3) = -3*E_2(0) and E_2(4) = - 6*E_2(0) - 5*E_2(1). More examples are given below. The precise result is E_2(k) = A121867(k) * E_2(0) - A121868(k) * E_2(1). For similar results see A143628. The decimal expansions of E_2(0) and E_2(1) are given in A143623 and A143624 respectively. - Peter Bala, Aug 28 2008 E.g.f.: A(x) = -sin(exp(x)-1). a(n) = Sum_{k=0..floor(n/2)} stirling2(n,2*k+1)*(-1)^(k+1). - Vladimir Kruchinin, Jan 26 2011 EXAMPLE From Peter Bala, Aug 28 2008: (Start) E_2(k) as a linear combination of E_2(i), i = 0..1. ============================ ..E_2(k)..|...E_2(0)..E_2(1) ============================ ..E_2(2)..|....-1.......1... ..E_2(3)..|....-3.......0... ..E_2(4)..|....-6......-5... ..E_2(5)..|....-5.....-23... ..E_2(6)..|....33.....-74... ..E_2(7)..|...266....-161... ..E_2(8)..|..1309......57... ..E_2(9)..|..4905....3466... (End) MAPLE # Maple code for A024430, A024429, A121867, A121868. M:=30; a:=array(0..100); b:=array(0..100); c:=array(0..100); d:=array(0..100); a[0]:=1; b[0]:=0; c[0]:=1; d[0]:=0; for n from 1 to M do a[n]:=add(binomial(n-1, k)*b[k], k=0..n-1); b[n]:=add(binomial(n-1, k)*a[k], k=0..n-1); c[n]:=add(binomial(n-1, k)*d[k], k=0..n-1); d[n]:=-add(binomial(n-1, k)*c[k], k=0..n-1); od: ta:=[seq(a[n], n=0..M)]; tb:=[seq(b[n], n=0..M)]; tc:=[seq(c[n], n=0..M)]; td:=[seq(d[n], n=0..M)]; # Code based on Stirling transform: stirtr:= proc(p) proc(n) option remember;             add(p(k) *Stirling2(n, k), k=0..n) end          end: a:= stirtr(n-> (I^(n+1) + (-I)^(n+1))/2): seq(a(n), n=0..30);  # Alois P. Heinz, Jan 29 2011 MATHEMATICA stirtr[p_] := Module[{f}, f[n_] := f[n] = Sum[p[k]*StirlingS2[n, k], {k, 0, n}]; f]; a = stirtr[(I^(#+1)+(-I)^(#+1))/2&]; Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Mar 11 2014, after Alois P. Heinz *) Table[Im[BellB[n, -I]], {n, 0, 25}] (* Vladimir Reshetnikov, Oct 22 2015 *) PROG (PARI) a(n) = sum(k=0, n\2, (-1)^(k+1)*stirling(n, 2*k+1, 2)); vector(30, n, a(n-1)) \\ G. C. Greubel, Oct 09 2019 (MAGMA) [(&+[(-1)^(k+1)*StirlingSecond(n, 2*k+1): k in [0..Floor(n/2)]]): n in [0..30]]; // G. C. Greubel, Oct 09 2019 (Sage) [sum((-1)^(k+1)*stirling_number2(n, 2*k+1) for k in (0..floor(n/2))) for n in (0..30)] # G. C. Greubel, Oct 09 2019 (GAP) List([0..30], n-> Sum([0..Int(n/2)], k-> (-1)^(k+1)* Stirling2(n, 2*k+1)) ); # G. C. Greubel, Oct 09 2019 CROSSREFS Cf. A121867, A024430, A024429. Cf. A000587, A143623, A143624, A143628, A143631. - Peter Bala, Aug 28 2008 Sequence in context: A125955 A103478 A327976 * A111584 A225266 A293426 Adjacent sequences:  A121865 A121866 A121867 * A121869 A121870 A121871 KEYWORD sign AUTHOR N. J. A. Sloane, Sep 05 2006 STATUS approved

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Last modified January 21 08:09 EST 2020. Contains 331104 sequences. (Running on oeis4.)