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A180089 Semiprimes which are the sum of three distinct positive cubes in two or more distinct ways. 3

%I

%S 1366,1457,1793,1945,3599,4105,5435,7379,8315,9017,10261,10963,11773,

%T 12706,13957,15163,15371,15553,15751,15758,16271,17263,17354,17947,

%U 18649,19027,19369,19657,19729,19774,19781,19907,21026,21167,22411

%N Semiprimes which are the sum of three distinct positive cubes in two or more distinct ways.

%C 2^3+3^3+11^3=5^3+8^3+9^3=1366=2*683, 1^3+5^3+11^3=6^3+8^3+9^3=1457=31*47,..

%H Chai Wah Wu, <a href="/A180089/b180089.txt">Table of n, a(n) for n = 1..10000</a>

%t f[n_]:=Last/@FactorInteger[n]=={1,1}; lst={};Do[Do[Do[If[f[p=a^3+b^3+c^3],AppendTo[lst,p]],{c,b-1,1,-1}],{b,a-1,1,-1}],{a,55}];lst1=Sort@lst; lst={};Do[If[lst1[[n]]==lst1[[n+1]],AppendTo[lst,lst1[[n]]]],{n,Length[lst1]-1}];lst

%Y Cf. A011541, A024974, A025400, A122723, A180088

%K nonn

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, Aug 09 2010

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Last modified August 5 03:00 EDT 2021. Contains 346457 sequences. (Running on oeis4.)