OFFSET
1,1
COMMENTS
The greatest common divisor of the three cubes must be 1, but they need not be pairwise coprime.
LINKS
EXAMPLE
a(3)=17 is in the sequence because 17 = 1^3 + 2^3 + 2^3 with gcd(1,2,2)=1.
MAPLE
N:= 1000: # for all terms <= N
S:= {seq(seq(seq(x^3+y^3+z^3, z=select(t -> igcd(x, y, t)=1, [$y..floor((N-x^3-y^3)^(1/3))])), y=x..floor(((N-x^3)/2)^(1/3))), x=1..floor((N/3)^(1/3)))}:
sort(convert(S, list));
PROG
(PARI) list(lim)=my(v=List(), s, g, x3); lim\=1; if(lim<3, return([])); for(x=1, sqrtnint(lim\3, 3), x3=x^3; for(y=x, sqrtnint((lim-x3)\2, 3), s=x3+y^3; g=gcd(x, y); if(g>1, for(z=y, sqrtnint(lim-s, 3), if(gcd(g, z)==1, listput(v, s+z^3))), for(z=y, sqrtnint(lim-s, 3), listput(v, s+z^3))))); Set(v) \\ Charles R Greathouse IV, May 18 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel, May 17 2020
STATUS
approved