A257757 Quasi-Carmichael numbers to exactly seven bases.

777923, 1030189, 1060459, 4903309, 5493247, 5659637, 6431071, 6673087, 6778969, 9790577, 11390429, 11860969, 12053263, 12390319, 12602059, 21215011, 21842629, 22991989, 24005239, 39339667, 39929437, 40080661, 40761169, 42314449, 50979479, 51876007, 54345943

Offset: 1

Author

Tim Johannes Ohrtmann, May 12 2015

Keywords

• nonn

Comments

All known terms have only two prime factors, one slightly larger than the other.

a(435) = 7523021437 = 1597 * 1933 * 2437 is the first term which has more than two prime factors. - Hiroaki Yamanouchi, Sep 28 2015

a(5586) > 10^12. - Hiroaki Yamanouchi, Sep 28 2015

Examples

			a(1) = 777923 because this is the first squarefree composite number n such that exactly seven integers b except 0 exist such that for every prime factor p of n, p+b divides n+b (-879, -878, -875, -872, -867, -863, -839): 777923=881*883 and 2, 4 both divide 777044 and 3, 5 both divide 777045 and 6, 8 both divide 777048 and 9, 11 both divide 777051 and 14, 16 both divide 777056 and 18, 20 both divide 777060 and 42, 44 both divide 777084.
		

Links

• Hiroaki Yamanouchi, Table of n, a(n) for n = 1..5885

Crossrefs

Cf. A257750 (every number of bases).

Cf. A257751, A257752, A257753, A257754, A257755, A257756, A258842 (1 to 6 and 8 bases).

Cf. A257758 (first occurrences).

Programs

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==7, print1(n, ", ")))))

Extensions

a(16)-a(27) from Hiroaki Yamanouchi, Sep 26 2015