OFFSET
1,1
COMMENTS
p is a base-b Wieferich prime iff b^(p-1) == 1 (mod p^2).
Records in A248865 sometimes arise when all the b values (bases) are powers of the same small integer. By excluding powers, we find primes that are Wieferich in many "independent" ways.
EXAMPLE
Prime 5107 is Wieferich to six bases (under 5107), namely 560, 1209, 1779, 2621, 4295, 4361, none of which are perfect powers. A prime such as 1093 is Wieferich to ten bases, namely 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024; however, when dismissing perfect powers, only one of the ten bases is left. In fact, no prime less than 5107 has six or more bases when perfect powers are dismissed, so 5107 sets a record and is included in this sequence.
PROG
(PARI) r=-oo; forprime(p=2, , i=sum(b=2, p-1, !ispower(b) && Mod(b, p^2)^(p-1)==1); if(i>r, print1(p, ", "); r=i))
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jeppe Stig Nielsen, Sep 06 2020
EXTENSIONS
a(8)-a(9) from Kellen Shenton added by Jeppe Stig Nielsen, Sep 12 2020
STATUS
approved