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A339533 Numbers b > 1 such that the smallest four primes, i.e., 2, 3, 5 and 7 are base-b Wieferich primes. 6

%I

%S 557,901,1549,2449,4049,5293,5849,6193,7057,7957,8801,9701,12349,

%T 13249,14093,14993,15857,16201,16757,18001,19601,20501,21149,21493,

%U 22049,23257,23293,24893,25057,25793,26657,27557,28549,30349,31949,32849,33301,34201,35801

%N Numbers b > 1 such that the smallest four primes, i.e., 2, 3, 5 and 7 are base-b Wieferich primes.

%t Select[Range[2, 36000], Function[b, AllTrue[{2, 3, 5, 7}, PowerMod[b, (# - 1), #^2] == 1 &]]] (* _Michael De Vlieger_, Dec 10 2020 *)

%o (PARI) is(n) = forprime(p=1, 7, if(Mod(n, p^2)^(p-1)!=1, return(0))); 1

%Y Cf. A256236. Row 1 of A319061.

%Y Cf. smallest k primes are base-b Wieferich primes: A339531 (k=2), A339532 (k=3), A339534 (k=5), A339535 (k=6), A339536 (k=7), A339537 (k=8).

%K nonn

%O 1,1

%A _Felix Fröhlich_, Dec 08 2020

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Last modified December 2 03:43 EST 2021. Contains 349437 sequences. (Running on oeis4.)