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A127070
Define an array by d(m, 0) = 1, d(m, 1) = m; d(m, k) = (m - k + 1) d(m+1, k-1) - (k-1) (m+1) d(m+2, k-2). Sequence gives d(4,n).
2
1, 4, 10, -24, -420, -960, 22680, 201600, -1496880, -36288000, 64864800, 7823692800, 25297272000, -2092278988800, -18988521552000, 690452066304000, 11457025515936000, -277436193914880000, -7430805000755136000, 133809610449715200000, 5500591866494524800000, -76432049488877322240000
OFFSET
0,2
REFERENCES
V. van der Noort and N. J. A. Sloane, Paper in preparation, 2007.
LINKS
MAPLE
T:= proc(n, k) option remember;
if k=0 then 1
elif k=1 then n
else (n-k+1)*T(n+1, k-1) - (k-1)*(n+1)*T(n+2, k-2)
fi; end:
seq(T(4, n), n=0..25); # G. C. Greubel, Jan 29 2020
MATHEMATICA
T[n_, k_]:= T[n, k]= If[k==0, 1, If[k==1, n, (n-k+1)*T[n+1, k-1] - (k-1)*(n+1)* T[n+2, k-2]]]; Table[T[4, n], {n, 0, 25}] (* G. C. Greubel, Jan 29 2020 *)
PROG
(PARI) T(n, k) = if(k==0, 1, if(k==1, n, (n-k+1)*T(n+1, k-1) - (k-1)*(n+1)*T(n+2, k-2) ));
vector(25, n, T(4, (n-1)) ) \\ G. C. Greubel, Jan 29 2020
(Magma)
function T(n, k)
if k eq 0 then return 1;
elif k eq 1 then return n;
else return (n-k+1)*T(n+1, k-1) - (k-1)*(n+1)*T(n+2, k-2);
end if; return T; end function;
[T(4, n): n in [0..25]]; // G. C. Greubel, Jan 29 2020
(Sage)
@CachedFunction
def T(n, k):
if (k==0): return 1
elif (k==1): return n
else: return (n-k+1)*T(n+1, k-1) - (k-1)*(n+1)*T(n+2, k-2)
[T(4, n) for n in (0..25)] # G. C. Greubel, Jan 29 2020
CROSSREFS
A column of A105937.
Sequence in context: A217696 A223014 A038783 * A365861 A107961 A051864
KEYWORD
sign
AUTHOR
Vincent v.d. Noort, Mar 21 2007
STATUS
approved