This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A257758 #19 Sep 27 2015 09:42:50 %S A257758 35,221,1517,60491,34933,189029,777923,182293,11618977,58076041, %T A257758 268926877,1047880741,342323563,447110449,2987821321,11951066641, %U A257758 19719180049,10178985781,249381206761,30512751277,190703385391,128931982141 %N A257758 Least Quasi-Carmichael number to exactly n bases. %C A257758 Is this sequence infinite? %C A257758 10^12 < a(23) <= 4361890724227, a(24) = 805822195351 and a(25) = 560433369241. %H A257758 Hiroaki Yamanouchi, <a href="/A257758/a257758.txt">upper bounds of a(1)-a(65) (a(n) <= 10^20)</a> %e A257758 a(4) = 60491 because this is the first squarefree composite number n such that exactly four integers except 0 exist such that for every prime factor p of n applies that p+b divides n+b (-239, -236, -231, -191): 60491=241*251 and 2, 12 both divide 60252 and 5, 15 both divide 60255 and 10, 20 both divide 60260 and 50, 60 both divide 60300. %o A257758 (PARI) for(d=1,9, n=1; until(k==d, n++; 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==d, print1(n,", ")))))) %Y A257758 Cf. A257750 (every number of bases). %Y A257758 Cf. A257751, A257752, A257753, A257754, A257755, A257756, A257757, A258842 (1 to 8 bases). %K A257758 nonn,more %O A257758 1,1 %A A257758 _Tim Johannes Ohrtmann_, May 12 2015 %E A257758 a(10)-a(22) from _Hiroaki Yamanouchi_, Sep 26 2015