A181375 Total number of positive integers below 10^n requiring 2 positive cubes in their representation as sum of cubes.

2, 9, 41, 202, 938, 4354, 20330, 94625, 439959, 2045048, 9500746, 44124084, 204883131, 951202028, 4415710979, 20497646229, 95146359635

Offset: 1

Author

Martin Renner, Jan 28 2011

Keywords

• nonn
• more

Comments

A061439(n) + a(n) + A181377(n) + A181379(n) + A181381(n) + A181400(n) + A181402(n) + A181404(n) + A130130(n) = A002283(n).

Links

• Eric Weisstein's World of Mathematics, Waring's Problem.

Crossrefs

Cf. A003325.

Programs

Maple

iscube:=proc(n) if root(n,3)=trunc(root(n,3)) then true; else false; fi; end:
isA003325:=proc(n) local x,y3; if iscube(n) then false; else for x from 1 do y3:=n-x^3; if y3A003325(k) then i:=i+1; fi; od: return(i); end:
for n from 1 do print(a(n)); od;

PARI

a(n)=my(N=10^n,v=List(),x3);sum(x=1,sqrtnint(N-1,3),x3=x^3;sum(y=1, min(sqrtnint(N-x3,3),x), !ispower(x3+y^3,3) && listput(v,x3+y^3))); #vecsort(v,,8) \\ Charles R Greathouse IV, Oct 16 2013

Extensions

a(6)-a(12) from Lars Blomberg, May 04 2011

a(13)-a(17) from Hiroaki Yamanouchi, Jul 12 2014