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Numbers that are not coprime to their 9's complement.
2

%I #21 Mar 20 2023 13:46:41

%S 3,6,9,11,12,15,18,21,22,24,27,30,33,36,39,42,44,45,48,51,54,55,57,60,

%T 63,66,69,72,75,77,78,81,84,87,88,90,93,96,99,102,105,108,111,114,117,

%U 120,123,126,129,132,135,138,141,144,147,148,150,153,156,159

%N Numbers that are not coprime to their 9's complement.

%C All multiples of 3 are in this sequence. Multiples of 11 are in this sequence if they have an even number of digits or if they are also multiples of 3.

%H Reinhard Zumkeller, <a href="/A201462/b201462.txt">Table of n, a(n) for n = 1..10000</a>

%e 22 is in the sequence because its 9's complement is 77 and gcd(22, 77) = 11 > 1.

%t (* First run the program for A061601 to define nineComplement *) Select[Range[200], GCD[#, nineComplement[#]] > 1 &]

%o (Magma) [n: n in [3..159] | Gcd(10^#Intseq(n)-1,n) gt 1]; // _Bruno Berselli_, Dec 02 2011

%o (Haskell)

%o a201462 n = a201462_list !! (n-1)

%o a201462_list = [x | x <- [1..], gcd x (a061601 x) > 1]

%o -- _Reinhard Zumkeller_, Dec 03 2011

%Y Cf. A061601 (9's complement of n), A192817 (complement).

%K nonn,easy,base

%O 1,1

%A _Alonso del Arte_, Dec 01 2011