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Search: id:A143817
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| A143817 |
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Let A(0)=1, B(0)=0 and C(0)=0. Let B(n+1) = sum {k = 0..n) binomial(n,k)*A(k), C(n+1) = sum {k = 0..n) binomial(n,k)*B(k) and A(n+1) = sum {k = 0..n) binomial(n,k)*C(k). This entry gives the sequence C(n). |
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10
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| 0, 0, 1, 3, 7, 16, 46, 203, 1178, 7242, 43786, 259634, 1540540, 9414639, 61061613, 428890726, 3266930298, 26581123093, 226393705465, 1986997358251, 17827284972818, 163278469610570, 1531115974317975, 14771302315885372
(list; graph; listen)
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OFFSET
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0,4
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COMMENT
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Compare with A024429 and A024430.
This sequence and its companion sequences A(n) = A143815 and B(n) = A143816 may be viewed as generalisations of the Bell numbers A000110. Define R(n) = sum {k = 0..inf} (3k)^n/(3k)! for n = 0,1,2,... . Then the real number R(n) is an integral linear combination of R(0) = 1 + 1/3! + 1/6! + ...., R(2) - R(1) = 1/1! + 1/4! + 1/7! + ... and R(1) = 1/2! + 1/5! + 1/8! + ... . Some examples are given below. The precise result is R(n) = A(n)*R(0) + B(n)*R(1) + C(n)*(R(2)-R(1)). This generalises the Dobinski relation for the Bell numbers: sum {k = 0..inf} k^n/k! = A000110(n)*exp(1). See A143815 for more details. Compare with A143628 - A143631. The decimal expansions of R(0), R(2) - R(1) and R(1) may be found in A143819, A143820 and A143821 respectively.
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FORMULA
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a(n) = sum {k = 0..floor((n-2)/3)} Stirling2(n,3k+2). Let w = exp(2*Pi*i/3) and set F(x) = (exp(x) + w*exp(w*x) + w^2*exp(w^2*x))/3 = x^2/2! + x^5/5! + x^8/8! + ... . Then the e.g.f. for the sequence is F(exp(x)-1). A143815(n) + A143816(n) + A143817(n) = Bell(n).
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EXAMPLE
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R(n) as a linear combination of R(0),R(1)
and R(2) - R(1).
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..R(n)..|.....R(0).....R(1)...R(2)-R(1)
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..R(3)..|.......1........1........3....
..R(4)..|.......6........2........7....
..R(5)..|......25.......11.......16....
..R(6)..|......91.......66.......46....
..R(7)..|.....322......352......203....
..R(8)..|....1232.....1730.....1178....
..R(9)..|....5672.....8233.....7242....
..R(10).|...32202....39987....43786....
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MAPLE
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(1)
M:=24: a:=array(0..100): b:=array(0..100): c:=array(0..100):
a[0]:=1: b[0]:=0: c[0]:=0:
for n from 1 to M do
b[n]:=add(binomial(n-1, k)*a[k], k=0..n-1);
c[n]:=add(binomial(n-1, k)*b[k], k=0..n-1);
a[n]:=add(binomial(n-1, k)*c[k], k=0..n-1);
end do:
A143817:=[seq(c[n], n=0..M)];
(2)
with(combinat):
seq(sum(stirling2(n, 3*i+2), i = 0..floor((n-2)/3)), n = 0..24);
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CROSSREFS
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A000110, A024429, A024430, A143628, A143629, A143630, A143631, A143815, A143816, A143818, A143819, A143820, A143821.
Sequence in context: A000674 A129045 A005312 this_sequence A000963 A133593 A087749
Adjacent sequences: A143814 A143815 A143816 this_sequence A143818 A143819 A143820
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KEYWORD
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easy,nonn
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AUTHOR
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Peter Bala (pbala(AT)toucansurf.com), Sep 03 2008
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