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 A242830 For p = prime(n), a(n) = number of bases 1 < b < p such that b^(p-1) == 1 (mod p^2). 13
 0, 0, 0, 0, 2, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 0, 2, 0, 1, 0, 0, 1, 0, 1, 0, 1, 1, 2, 2, 1, 0, 0, 1, 0, 2, 0, 0, 0, 1, 1, 0, 1, 1, 2, 1, 0, 2, 1, 0, 1, 0, 1, 1, 3, 0, 0, 1, 1, 1, 1, 0, 2, 0, 3, 0, 2, 2, 2, 2, 2, 1, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 0, 1, 2, 0, 0, 4, 0, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS a(n) > 0 if and only if p is in A134307. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 MAPLE A242830:= proc(n) local p; p:= ithprime(n); numboccur(1, [seq(b &^ (p-1) mod p^2, b=2..p-1)]); end proc; seq(A242830(n), n=1..1000); # Robert Israel, Jul 16 2014 MATHEMATICA a[n_] := With[{p = Prime[n]}, Length@Select[Range[2, p-1], PowerMod[#, p-1, p^2] == 1&]]; Table[a[n], {n, 1, 100}] (* Jean-François Alcover, Jan 27 2023 *) PROG (PARI) i=0; forprime(p=2, 10^3, a=2; while(a

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Last modified June 7 12:23 EDT 2023. Contains 363157 sequences. (Running on oeis4.)