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%I #4 May 26 2019 15:01:04
%S 1451,1482,3145,3147,3277,3365,3376,4339,4357,4365,4393,4625,5649,
%T 5850,7282,7624,8641,8956,8957,9149,9449,10040,10093,10538,10835,
%U 10889,12001,12476,12907,13253,14005,14027,14032,14500,15029,15229,15797,15857,16249,16757
%N Bases b where exactly seven primes p with p < b exist such that p is a base-b Wieferich prime.
%C Numbers n such that A255920(n) = 7.
%o (PARI) is(n) = my(i=0); forprime(p=1, n-1, if(Mod(n, p^2)^(p-1)==1, i++)); i==7
%Y Cf. A255920.
%Y Cf. bases b with exactly k base-b Wieferich primes less than b: A255921 (k=0), A255922 (k=1), A255923 (k=2), A255924 (k=3), A255925 (k=4), A325881 (k=5), A325882 (k=6), A325884 (k=8), A325885 (k=9), A325886 (k=10).
%K nonn
%O 1,1
%A _Felix Fröhlich_, May 26 2019