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A158248 Composite numbers with primitive root 10.

%I A158248 #56 Nov 24 2021 06:03:51
%S A158248 49,289,343,361,529,841,2209,2401,3481,3721,4913,6859,9409,11881,
%T A158248 12167,12769,16807,17161,22201,24389,27889,32041,32761,37249,49729,
%U A158248 52441,54289,66049,69169,72361,83521,97969
%N A158248 Composite numbers with primitive root 10.
%C A158248 Previous name was: Numbers m whose reciprocal generates a repeating decimal fraction with period phi(m) and m/2 < phi(m) < m-1.
%C A158248 All terms are proper powers of full reptend primes (A001913).
%C A158248 This sequence does not contain every proper power of every term in A001913, for example, A001913 has 487 as its 26th term, but since 10 is not a primitive root of 487^2, 487^2 is not a term of this sequence. - _Robert Hutchins_, Oct 14 2021
%C A158248 A shorter description appears to be "Composite numbers with primitive root 10". - _Arkadiusz Wesolowski_, Jul 04 2012 (The two definitions certainly produce the same terms up through 83521. - _N. J. A. Sloane_, Jul 05 2012)
%H A158248 Ray Chandler, <a href="/A158248/b158248.txt">Table of n, a(n) for n = 1..1000</a>
%p A158248 select(n -> not isprime(n) and numtheory:-primroot(9,n) = 10,[$2..10000]);
%p A158248 # _N. J. A. Sloane_, Jul 05 2012
%t A158248 Select[Range[10^5], GCD[10, #] == 1 && #/2 < MultiplicativeOrder[10, #] < # - 1 &] (* _Ray Chandler_, Oct 17 2012 *)
%Y A158248 Cf. A007732, A001913, A046145, A046146.
%Y A158248 Subsequence of A244623.
%Y A158248 Subsequence of A167797.
%Y A158248 Cf. A108989 (for base 2), A346316 (for base 6).
%K A158248 nonn,base
%O A158248 1,1
%A A158248 _Robert Hutchins_, Mar 15 2009
%E A158248 More terms from _Robert Hutchins_, Mar 21 2009
%E A158248 Entry revised by _N. J. A. Sloane_, Jul 05 2012
%E A158248 New name (using comment by _Arkadiusz Wesolowski_) from _Joerg Arndt_, Nov 22 2021