cp's OEIS Frontend

A038593 Differences between positive cubes in 1, 2 or 3 ways: union of A014439, A014440 and A014441.

%I A038593 #13 Oct 19 2017 03:13:48
%S A038593 7,19,26,37,56,61,63,91,98,117,124,127,152,169,189,208,215,217,218,
%T A038593 271,279,296,316,331,335,342,386,387,397,448,469,485,488,504,511,513,
%U A038593 547,602,604,631,657,665,702,721,728,784,817,819,866,875,919,936,973,988
%N A038593 Differences between positive cubes in 1, 2 or 3 ways: union of A014439, A014440 and A014441.
%H A038593 Robert Israel, <a href="/A038593/b038593.txt">Table of n, a(n) for n = 1..10000</a>
%p A038593 N:= 1000: # to get all terms <= N
%p A038593 X:= floor(sqrt(N/3)):
%p A038593 V:= Vector(N):
%p A038593 for x from 2 to X do
%p A038593   if x^3 > N then
%p A038593      y0:= iroot(x^3-N,3);
%p A038593      if x^3 - y0^3 > N then y0:= y0+1 fi;
%p A038593   else y0:= 1 fi;
%p A038593   for y from y0 to x-1 do
%p A038593      V[x^3 - y^3] := V[x^3 - y^3]+1
%p A038593   od
%p A038593 od:
%p A038593 select(t -> V[t] <= 3 and V[t]>=1, [$1..N]); # _Robert Israel_, Dec 10 2015
%t A038593 r = 988; p = 3; Sort@Drop[Flatten@Select[Tally@Reap[Do[n = i^p - j^p; If[n <= r, Sow[n]], {i, Ceiling[(r/p)^(1/(p - 1))]}, {j, i}]][[2, 1]], 0 < #[[2]] < 4 &], {2, -1, 2}] (* _Arkadiusz Wesolowski_, Dec 10 2015 *)
%Y A038593 Cf. A038594, A038595, A038596, A038597, A038598.
%K A038593 nonn
%O A038593 1,1
%A A038593 _Jeff Burch_
%E A038593 Corrected by _Don Reble_, Nov 19 2006