OFFSET
1,1
COMMENTS
Is this sequence infinite?
10^12 < a(23) <= 4361890724227, a(24) = 805822195351 and a(25) = 560433369241.
LINKS
Hiroaki Yamanouchi, upper bounds of a(1)-a(65) (a(n) <= 10^20)
EXAMPLE
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.
PROG
(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, ", "))))))
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Tim Johannes Ohrtmann, May 12 2015
EXTENSIONS
a(10)-a(22) from Hiroaki Yamanouchi, Sep 26 2015
STATUS
approved