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A038862 Numbers ending with '7' that are the difference of two positive cubes. 1


%S 7,37,117,127,217,387,397,547,657,817,1027,1197,1267,1387,1647,1657,

%T 1727,2107,2437,2457,2717,2977,3087,3367,3997,4167,4447,4697,4977,

%U 5167,5677,5707,6327,6347,6487,6517,7057,7317,7657,7957,8587,8937,9197,9317

%N Numbers ending with '7' that are the difference of two positive cubes.

%H Robert Israel, <a href="/A038862/b038862.txt">Table of n, a(n) for n = 1..10000</a>

%p filter:= proc(n) local t,y,r;

%p for t in sort(convert(numtheory:-divisors(n),list)) do

%p r:= 12*n*t-3*t^4;

%p if r < 0 then return false fi;

%p if not issqr(r) then next fi;

%p y:= (sqrt(r)-3*t^2)/(6*t);

%p if y::posint then return true fi

%p od;

%p false

%p end proc:

%p select(filter, [seq(i,i=7..10000,10)]); # _Robert Israel_, Aug 08 2019

%t With[{nn=60},Select[Union[#[[2]]-#[[1]]&/@Subsets[Range[nn]^3,{2}]],Mod[#,10] == 7&&#<nn^3-(nn-1)^3&]] (* _Harvey P. Dale_, Jan 12 2022 *)

%Y Cf. A181123.

%K nonn,base

%O 1,1

%A _Jeff Burch_

%E Name corrected by _Robert Israel_, Aug 08 2019

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Last modified February 7 15:43 EST 2023. Contains 360127 sequences. (Running on oeis4.)