OFFSET
0,2
COMMENTS
Write n (uniquely) as n = C(n_t,t) + C(n_{t-1},t-1) + ... + C(n_v,v) where n_t > n_{t-1} > ... > n_v >= v >= 1. Then K_t(n) = C(n_t,t-1) + C(n_{t-1},t-2) + ... + C(n_v,v-1).
REFERENCES
D. E. Knuth, The Art of Computer Programming, Vol. 4, Fascicle 3, Section 7.2.1.3, Table 3.
MAPLE
lowpol := proc(n, t) local x::integer ; x := floor( (n*factorial(t))^(1/t)) ; while binomial(x, t) <= n do x := x+1 ; od ; RETURN(x-1) ; end: C := proc(n, t) local nresid, tresid, m, a ; nresid := n ; tresid := t ; a := [] ; while nresid > 0 do m := lowpol(nresid, tresid) ; a := [op(a), m] ; nresid := nresid - binomial(m, tresid) ; tresid := tresid-1 ; od ; RETURN(a) ; end: K := proc(n, t) local a ; a := C(n, t) ; add( binomial(op(i, a), t-i), i=1..nops(a)) ; end: A123572 := proc(n) K(n, 3) ; end: for n from 0 to 80 do printf("%d, ", A123572(n)) ; od ; # R. J. Mathar, May 18 2007
MATHEMATICA
lowpol[n_, t_] := Module[{x}, x = Floor[(n*t!)^(1/t)]; While[Binomial[x, t] <= n, x = x + 1]; x - 1];
c[n_, t_] := Module[{n0 = n, t0 = t, m, a = {}}, While[n0 > 0, m = lowpol[n0, t0]; a = Append[a, m]; n0 = n0 - Binomial[m, t0]; t0 = t0 - 1]; a];
K[n_, t_] := Module[{a}, a = c[n, t]; Sum[Binomial[a[[i]], t - i], {i, 1, Length[a]}]];
A123572[n_] := K[n, 3];
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 12 2006
EXTENSIONS
More terms from R. J. Mathar, May 18 2007
STATUS
approved