OFFSET
0,1
LINKS
Chris Thompson, What is the next one? [primes isolated from squarefrees], SeqFan list.
EXAMPLE
a(0)=2 is the least prime and it is at distance 1 from the nearest squarefree numbers (1 and/or 3).
a(1)=17 is the least prime that has no squarefree neighbor: both 16 and 18 are divisible by a square; the nearest squarefree numbers, 15 and 19, are both at distance 2.
a(2)=727 is the least prime p such that p-2 and p+1 are (two consecutive terms) in A068781, namely A068781(75..76).
a(3)=47527 is the least prime p such that p-3 and p+1 are (two consecutive terms) in A070258, namely A070258(878..879).
a(4)=29002021 is the least prime p such that p-4 and p+1 are (two consecutive terms) in A070284.
a(5)=494501773 is the least prime p such that p-5 and p+1 are (two consecutive terms) in A078144.
PROG
(PARI) a(n)=forprime(p=n, , for(s=1, n, (issquarefree(p-s)||issquarefree(p+s)) && next(2)); return(p))
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Juri-Stepan Gerasimov and M. F. Hasler, Jan 01 2016
EXTENSIONS
a(4) corrected and a(5) computed by Christopher E. Thompson, Jan 20 2016
a(6)-a(7) from Bert Dobbelaere, Jan 28 2019
STATUS
approved