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 A278611 Bases b > 1 that set a new record for the size of the smallest base-b Wieferich prime. 2
 2, 6, 34 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that A039951(n) reaches a new record value. a(1) = 2. Thereafter smallest number x that occurs later in column 1 of A244249 than any y with 1 < y < x. Let b(n) be the sequence of corresponding smallest Wieferich primes. b(1)-b(3) are 1093, 66161 and 46145917691, respectively (cf. A307220). No term is a perfect power, since then its smallest Wieferich prime is at most the size of the smallest Wieferich prime of the base that is raised to a power. a(4) is either 47, 72 or 139, depending on which of those bases is the smallest where any Wieferich prime exists. The smallest base-139 Wieferich prime is 1822333408543 and any Wieferich primes in bases 47 and 72 are larger than 1.07*10^14 (cf. Fischer). LINKS R. Fischer, Thema: Fermatquotient B^(P-1) == 1 (mod P^2) EXAMPLE a(2) = 6, since the smallest base-6 Wieferich prime is 66161 and that prime is the second term with a record value in A039951. PROG (PARI) smallest_w_prime(n) = forprime(p=1, , if(Mod(n, p^2)^(p-1)==1, return(p))) my(r=0, b=2); while(1, if(smallest_w_prime(b) > r, print1(b, ", "); r=smallest_w_prime(b)); b++) CROSSREFS Cf. A039951, A244249, A307220. Sequence in context: A005161 A062970 A259436 * A088125 A064940 A105142 Adjacent sequences:  A278608 A278609 A278610 * A278612 A278613 A278614 KEYWORD nonn,hard,more,bref AUTHOR Felix Fröhlich, Nov 23 2016 STATUS approved

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Last modified June 24 23:16 EDT 2021. Contains 345445 sequences. (Running on oeis4.)