A231472 - OEIS

%I #15 Mar 02 2018 18:19:55

%S 11,11,11,11,11,11,11,11,11,11,10,11,11,11,11,11,11,11,11,11,11,9,11,

%T 11,11,11,11,11,11,11,11,11,10,11,11,11,11,11,11,11,11,11,11,9,11,11,

%U 11,11,11,11,11,11,11,11,9,11,11,11,11,11,11,11,11,11,11,7,11,11,11,11,11,11,11,11,11,11,10

%N Largest integer less than 12 and coprime to n.

%C Values in this sequence are 1, 5, 7, 8, 9, 10, and 11; the average value is 3569/330 = 10.81515.... - _Charles R Greathouse IV_, Aug 19 2016

%H Harvey P. Dale, <a href="/A231472/b231472.txt">Table of n, a(n) for n = 1..1000</a>

%e a(1..10)=11 because this is the largest integer less than 12 and it is coprime to n=1,...,10.

%e a(11)=10 because 11 is not coprime to 11 but 10 is.

%e a(22)=9 because 11 and 10 are not coprime to 22=2*11.

%e a(2310)=1 because 2310=2*3*5*7*11 is not coprime to any number n>1, n<12.

%t Table[SelectFirst[Range[11,1,-1],CoprimeQ[#,n]&],{n,80}] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Mar 02 2018 *)

%o (PARI) a(n,m=12)=for(k=1,m,gcd(n,m-k)==1&&return(m-k))

%Y Cf. A231471 (analog for 11), A231470 (analog for 10), A231155.

%K nonn,easy

%O 1,1

%A _M. F. Hasler_, Nov 09 2013