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A101902
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Numbers n that are not of the form ab+bc+cd+de+ea with a,b,c,d,e>0.
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0
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1, 2, 3, 4, 6, 8, 12, 14, 18, 30, 38, 42, 62
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Conjecture that this sequence is complete. Note that, except for n=1 and n=2, n-1 is prime. The case of the 3-term binary form is treated in A025052. For the 4-term case, ab+bc+cd+da, no prime is representable because the 4 terms factor as (a+c)(b+d).
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MATHEMATICA
| nn=100; cnt5=Table[0, {nn}]; Do[n=a*b+b*c+c*d+d*e+e*a; If[n<=nn, cnt5[[n]]++ ], {a, nn}, {b, a, nn}, {c, b, nn}, {d, c, nn}, {e, d, nn}]; Flatten[Position[cnt5, 0]]
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CROSSREFS
| Cf. A025052 (n not of form ab + bc + ca).
Sequence in context: A029449 A028815 A014423 * A114312 A095041 A178751
Adjacent sequences: A101899 A101900 A101901 * A101903 A101904 A101905
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KEYWORD
| nonn
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AUTHOR
| T. D. Noe (noe(AT)sspectra.com), Dec 20 2004
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