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Pseudoprimes to base 7, written in base 7.
7

%I #36 Jul 25 2021 02:40:23

%S 6,34,643,1431,2023,2245,3136,5215,6061,6601,10121,12361,16123,20032,

%T 25345,33155,41545,42601,42652,44122,45406,50026,54561,56035,66522,

%U 66666,105403,110254,112612,113345,113356,123616,135206,140011,151142,151354,153022,153101,153352,155554

%N Pseudoprimes to base 7, written in base 7.

%H Amiram Eldar, <a href="/A262104/b262104.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A007093(A005938(n)).

%t base = 7; t = {}; n = 1;

%t While[Length[t] < 40, n++;

%t If[! PrimeQ[n] && PowerMod[base, n - 1, n] == 1,

%t AppendTo[t, FromDigits@IntegerDigits[n, 7]]]]; t

%t FromDigits[IntegerDigits[#,7]]&/@Select[Range[40000],CompositeQ[#] && PowerMod[ 7,#-1,#]==1&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Feb 24 2018 *)

%o (PARI) lista(nn, b=7) = {for (n=1, nn, if (Mod(b, n)^(n-1)==1 && !ispseudoprime(n) && n>1, print1(subst(Pol(digits(n,b), x), x, 10), ", ");););} \\ _Michel Marcus_, Sep 30 2015

%Y Cf. A005938 (pseudoprimes to base 7), A007093 (numbers in base 7).

%Y Cf. A258189, A262101, A262102, A262103, A262105, A262154.

%K nonn,base

%O 1,1

%A _Abdul Gaffar Khan_, Sep 11 2015