A181375 - OEIS

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

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OFFSET

1,1

COMMENTS

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

LINKS

Table of n, a(n) for n=1..17.

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

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 y3<x^3 then return false; elif iscube(y3) then return true; fi; od; fi; end:

a:=proc(n) local i, k; i:=0; for k from 2 to 10^n-1 do if isA003325(k) then i:=i+1; fi; od: return(i); end:

for n from 1 do print(a(n)); od;

PROG

(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

CROSSREFS

Cf. A003325.

Sequence in context: A362381 A292078 A270766 * A152052 A192661 A020038

Adjacent sequences: A181372 A181373 A181374 * A181376 A181377 A181378

KEYWORD

nonn,more

AUTHOR

Martin Renner, Jan 28 2011

EXTENSIONS

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

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

STATUS

approved