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A257752
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Quasi-Carmichael numbers to exactly two bases.
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10
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221, 323, 899, 935, 1105, 1147, 1271, 1591, 1595, 1885, 2093, 2465, 2821, 4757, 4807, 4991, 5609, 5963, 6497, 7081, 7843, 9991, 10373, 10403, 10961, 11009, 12319, 13843, 14111, 16031, 17155, 17399, 17653, 17963, 19043, 19721, 20701, 24613, 27331, 28417, 29341
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(1) = 221 because this is the first squarefree composite number n such that exactly two integers b except 0 exist such that for every prime factor p of n, p+b divides n+b (-11, -5): 221=13*17 and 2, 6 both divide 210 and 8, 12 both divide 216.
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PROG
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(PARI) for(n=2, 1000000, if(!isprime(n), if(issquarefree(n), f=factor(n); k=0; for(b=-(f[1, 1]-1), n, c=0; for(i=1, #f[, 1], if((n+b)%(f[i, 1]+b)>0, c++)); if(c==0, if(!b==0, k++))); if(k==2, print1(n, ", ")))))
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CROSSREFS
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Cf. A257750 (every number of bases).
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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