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A055745 Squarefree numbers not of form ab + bc + ca for 1<=a<=b<=c (probably the list is complete). 2
1, 2, 6, 10, 22, 30, 42, 58, 70, 78, 102, 130, 190, 210, 330, 462 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

Maohua Le, A note on positive integer solutions of the equation xy+yz+zx=n, Publ. Math. Debrecen 52 (1998) 159-165; Math. Rev. 98j:11016.

LINKS

Table of n, a(n) for n=1..16.

J. M. Borwein, Adventures with the OEIS: Five sequences Tony may like, Guttman 70th [Birthday] Meeting, 2015, revised May 2016.

J. M. Borwein, Adventures with the OEIS: Five sequences Tony may like, Guttman 70th [Birthday] Meeting, 2015, revised May 2016. [Cached copy, with permission]

J. Borwein and K.-K. S. Choi, On the representations of xy+yz+zx, Experimental Mathematics, 9 (2000), 153-158 (dvi, ps).

MATHEMATICA

solQ[n_, x_] := Reduce[1 <= y <= z && n == x*y + y*z + z*x, {y, z}, Integers] =!= False; solQ[n_] := Catch[xm = Ceiling[(n-1)/2]; For[x = 1, x <= xm, x++, Which[ solQ[n, x] === True, Throw[True], x == xm, Throw[False]]]] ; solQ[1] = False; Reap[ Do[ If[ SquareFreeQ[n], If[! solQ[n] , Print[n]; Sow[n]]], {n, 1, 500}]][[2, 1]] (* Jean-Fran├žois Alcover, Jun 15 2012 *)

CROSSREFS

Cf. A034168, A025052, A034169.

Sequence in context: A077064 A080715 A034168 * A182000 A167512 A055895

Adjacent sequences:  A055742 A055743 A055744 * A055746 A055747 A055748

KEYWORD

nonn,fini,nice

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified January 22 11:56 EST 2019. Contains 319363 sequences. (Running on oeis4.)