OFFSET
2,1
COMMENTS
Sequence begins with n = 2 because a(1) is undefined (sum of one positive cube cannot have exactly one prime factor, i.e., be prime).
FORMULA
a(n) = Min{x = (c_1)^3 + (c_2)^3 + ... + (c_n)^3 such that omega(x) = A001222(x) = n}.
EXAMPLE
MAPLE
isSumcPosC := proc(n, c, minb)
local nrt ;
if c = 1 then nrt := iroot(n, 3) ; if nrt^3 = n and n>= minb then true; else false; end if;
else for b from minb do if b^3 > n then return false; end if; if isSumcPosC(n-b^3, c-1, b) then return true; end if; end do: end if;
end proc:
A122733 := proc(n)
for a from 1 do if numtheory[bigomega](a) = n then if isSumcPosC(a, n, 1) then return a; end if; end if;
end do:
end proc:
for n from 2 do print(A122733(n)) ; end do: # R. J. Mathar, Dec 22 2010
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonathan Vos Post, Sep 23 2006
EXTENSIONS
a(17) from Giovanni Resta, Jun 13 2016
a(18)-a(21) more terms from R. J. Mathar, Jan 31 2017
STATUS
approved