login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A180089
Semiprimes which are the sum of three distinct positive cubes in two or more distinct ways.
3
1366, 1457, 1793, 1945, 3599, 4105, 5435, 7379, 8315, 9017, 10261, 10963, 11773, 12706, 13957, 15163, 15371, 15553, 15751, 15758, 16271, 17263, 17354, 17947, 18649, 19027, 19369, 19657, 19729, 19774, 19781, 19907, 21026, 21167, 22411
OFFSET
1,1
COMMENTS
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,..
MATHEMATICA
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
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved