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%I #15 Jun 07 2018 22:03:18
%S 1,10385,40486,13367790,1645333506,6692367336,11796759175
%N Multiplicative order of 5 (mod A123692(n)^2).
%C From _Eric Chen_, Jun 07 2018: (Start)
%C b known Wieferich primes in base b (multiplicative order of b mod these primes (also these primes^2)) (if the order is p-1, then b is a primitive root to mod this prime (but not mod this prime^2), see A055578)
%C 2 1093 (364), 3511 (1755)
%C 3 11 (5), 1006003 (1006002)
%C 4 1093 (182), 3511 (1755)
%C 5 2 (1), 20771 (10385), 40487 (40486), 53471161 (13367790), 1645333507 (1645333506), 6692367337 (6692367336), 188748146801 (11796759175)
%C 6 66161 (66160), 534851 (106970), 3152573 (788143)
%C 7 5 (4), 491531 (245765)
%C 8 3 (2), 1093 (364), 3511 (585)
%C 9 2 (1), 11 (5), 1006003 (503001)
%C 10 3 (1), 487 (486), 56598313 (56598312)
%C 11 71 (70)
%C 12 2693 (2692), 123653 (123652)
%C 13 2 (1), 863 (862), 1747591 (873795)
%C 14 29 (28), 353 (352), 7596952219 (7596952218)
%C 15 29131 (29130), 119327070011 (59663535005)
%C 16 1093 (91), 3511 (1755)
%C 17 2 (1), 3 (2), 46021 (7670), 48947 (24473), 478225523351 (478225523350)
%C 18 5 (4), 7 (3), 37 (36), 331 (110), 33923 (33922), 1284043 (428014)
%C 19 3 (1), 7 (6), 13 (12), 43 (42), 137 (68), 63061489 (63061488)
%C 20 281 (140), 46457 (46456), 9377747 (9377746), 122959073 (122959072)
%C 21 2 (1)
%C 22 13 (3), 673 (224), 1595813 (797906), 492366587 (246183293), 9809862296159 (44999368331)
%C 23 13 (6), 2481757 (827252), 13703077 (13703076), 15546404183 (7773202091), 2549536629329 (2549536629328)
%C 24 5 (2), 25633 (6408)
%C These orders n will satisfy that Phi_n(b) is divisible by p^2, where Phi is the cyclotomic polynomial. (Usually, Phi_n(b) is squarefree, but these are all exceptions; i.e., if p^2 divides Phi_n(b) (except the case p = 2, n = 2 and b == 3 (mod 4)), then p is a Wieferich prime in base b.)
%C (End)
%F a(n) = A305331(A123692(n)).
%o (PARI) v=[2, 20771, 40487, 53471161, 1645333507, 6692367337, 188748146801]; for(k=1, #v, print1(znorder(Mod(5, v[k]^2)), ", "))
%Y Cf. A123692, A211241, A305331, A305333.
%K nonn,hard,more
%O 1,2
%A _Felix Fröhlich_, May 30 2018
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