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If h_5(n) is the multiplicative order of 5 modulo n, r_5(n) is the number of cyclotomic cosets of 5 modulo n then, by the definition, n is an overpseudoprime of base 5 if h_5(n)*r_5(n)+1=n. These numbers are in A020231.In particular, if n is squarefree such that its prime factorization is
n=p_1*...*p_k, then n is overpseudoprime of base 5 iff h_5(p_1)=...=h_5(p_k).
E.g. since h_5(101)=h_5(251)=h_5(401)=25, then the number 101*251*401=10165751 is in the sequence.
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