A004825 Numbers that are the sum of at most 3 positive cubes.

0, 1, 2, 3, 8, 9, 10, 16, 17, 24, 27, 28, 29, 35, 36, 43, 54, 55, 62, 64, 65, 66, 72, 73, 80, 81, 91, 92, 99, 118, 125, 126, 127, 128, 129, 133, 134, 136, 141, 152, 153, 155, 160, 179, 189, 190, 192, 197, 216, 217, 218, 224, 225, 232, 243, 244, 250, 251, 253

Offset

1,3

Comments

Or: numbers which are the sum of 3 (not necessarily distinct) nonnegative cubes. - R. J. Mathar, Sep 09 2015

Deshouillers, Hennecart, & Landreau conjecture that this sequence has density 0.0999425... = lim_K Sum_{k=1..K} exp(c*rho(k,K)/K^2)/K where c = -gamma(4/3)^3/6 = -0.1186788..., K takes increasing values in A003418 (or, equivalently, A051451), and rho(k0,K) is the number of triples 1 <= k1,k2,k3 <= K such that k0 = k1^3 + k2^3 + k3^3 mod K. - Charles R Greathouse IV, Sep 16 2016

Links

Alois P. Heinz, Table of n, a(n) for n = 1..10000 (first 1000 terms from T. D. Noe)

Jean-Marc Deshouillers, François Hennecart, and Bernard Landreau, On the density of sums of three cubes, ANTS-VII (2006), pp. 141-155.

Index entries for sequences related to sums of cubes

Maple

isA004825 := proc(n)
    local x, y, zc ;
    for x from 0 do
        if 3*x^3 > n then
            return false;
        end if;
        for y from x do
            if x^3+2*y^3 > n then
                break;
            else
                zc := n-x^3-y^3 ;
                if zc >= y^3 and isA000578(zc) then
                    return true;
                end if;
            end if;
        end do:
    end do:
end proc:
A004825 := proc(n)
    option remember;
    local a;
    if n = 1 then
        0;
    else
        for a from procname(n-1)+1 do
            if isA004825(a) then
                return a;
            end if;
        end do:
    end if;
end proc:
seq(A004825(n), n=1..100) ; # R. J. Mathar, Sep 09 2015
# second Maple program:
b:= proc(n, i, t) option remember; n=0 or i>0 and t>0
      and (b(n, i-1, t) or i^3<=n and b(n-i^3, i, t-1))
    end:
a:= proc(n) option remember; local k;
      for k from 1+ `if`(n=1, -1, a(n-1))
      while not b(k, iroot(k, 3), 3) do od; k
    end:
seq(a(n), n=1..100);  # Alois P. Heinz, Sep 16 2016

Mathematica

q=7; imax=q^3; Select[Union[Flatten[Table[x^3+y^3+z^3, {x, 0, q}, {y, x, q}, {z, y, q}]]], #<=imax&] (* Vladimir Joseph Stephan Orlovsky, Apr 20 2011 *)

Prog

(PARI) list(lim)=my(v=List(), k, t); for(x=0, sqrtnint(lim\=1, 3), for(y=0, min(sqrtnint(lim-x^3, 3), x), k=x^3+y^3; for(z=0, min(sqrtnint(lim-k, 3), y), listput(v, k+z^3)))); Set(v) \\ Charles R Greathouse IV, Sep 14 2015

Crossrefs

A003072 is a subsequence.

Cf. A004999.

Column k=3 of A336820.

Sequence in context: A363088 A191159 A047360 * A272830 A028821 A337261

Adjacent sequences: A004822 A004823 A004824 * A004826 A004827 A004828

Keyword

nonn

Author

N. J. A. Sloane

Status

approved