Search: id:A122782
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%I A122782
%S A122782 1,4,10,15,20,65,124,190,217,310,435,561,781,1105,1541,1729,1891,2465,
%T A122782 2821,3565,3820,4123,4495,5461,5611,5662,5731,6601,6735,7449,7813,8029,
%U A122782 8290,8911,9881,10585,11041,11476,12801,13021,13333,13981,14981
%N A122782 Nonprimes n such that 5^n==5 (mod n).
%C A122782 Theorem: If both numbers q and 2q-1 are primes then n=q*(2q-1) is in 
               the sequence iff q=3 or q is of the form 10k+1. 15,1891,88831,146611,
               218791,721801,873181,... are such terms.
%t A122782 Select[Range[15000], ! PrimeQ[ # ] && Mod[5^#, # ] == Mod[5, # ] &]
%Y A122782 Cf. A005936.
%Y A122782 Sequence in context: A123925 A106668 A063295 this_sequence A153515 A005662 
               A099457
%Y A122782 Adjacent sequences: A122779 A122780 A122781 this_sequence A122783 A122784 
               A122785
%K A122782 nonn
%O A122782 1,2
%A A122782 Farideh Firoozbakht (mymontain(AT)yahoo.com), Sep 12 2006

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