A257756 - OEIS

A257756

Quasi-Carmichael numbers to exactly six bases.

189029, 404471, 424663, 2595221, 4140901, 4197377, 4347209, 4528159, 4566193, 4631023, 4708819, 4864411, 5175589, 5311729, 6380651, 6400819, 6426029, 7117783, 8173877, 8915971, 10080589, 10460869, 10671173, 11094661, 11538313

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..25.

EXAMPLE

a(1) = 189029 because this is the first squarefree composite number n such that exactly six integers b except 0 exist such that for every prime factor p of n, p+b divides n+b (-419, -414, -407, -389, -365, -309): 189029=421*449 and 2, 30 both divide 188610 and 7, 35 both divide 188615 and 14, 42 both divide 188622 and 32, 60 both divide 188640 and 56, 84 both divide 188664 and 112, 140 both divide 188720.

PROG

(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==6, print1(n, ", ")))))

CROSSREFS

Cf. A257750 (every number of bases).

Cf. A257751, A257752, A257753, A257754, A257755, A257757, A258842 (1, 2, 3, 4, 5, 7 and 8 bases).

Cf. A257758 (first occurrences).

Sequence in context: A233715 A110069 A006028 * A206018 A233873 A256768

Adjacent sequences: A257753 A257754 A257755 * A257757 A257758 A257759

KEYWORD

nonn

AUTHOR

Tim Johannes Ohrtmann, May 12 2015

STATUS

approved