A137371 a(n) = least semiprime such that all subsets of {a(1),...,a(n)} have a different sum.
4, 6, 9, 14, 22, 57, 111, 218, 445, 879, 1754, 3518, 7034, 14069, 28129, 56271, 112529, 225073, 450139, 900274, 1800559, 3601109, 7202221, 14404439, 28808881, 57617759, 115235531, 230471069, 460942121
Offset: 1
Links
- S. J. Benkoski and P. Erdős, On weird and pseudoperfect numbers, Math. Comp., 28 (1974), pp. 617-623. Alternate link; 1975 corrigendum
Programs
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Maple
isA001358 := proc(n) if numtheory[bigomega](n) = 2 then true; else false; fi ; end: setsum := proc(S) add(i,i=S) ; end: a := [4] : while true do for anxt from op(-1,a)+1 do if isA001358(anxt) then aset := combinat[powerset](convert(a,set) union {anxt} ); sset := {} ; for s in aset do sset := sset union { setsum(s) } ; od: if nops(sset) = nops(aset) then a := [op(a),anxt] ; print(a) ; break ; fi ; fi ; od: od: # R. J. Mathar
Extensions
More terms from R. J. Mathar
a(12)-a(29) from Donovan Johnson, Nov 11 2008