A132129 - OEIS

%I #12 Mar 06 2020 16:52:58

%S 2,19,19,577,7417,114229,2053313,42373937,987654103,25678048763,

%T 736867805209,23136292864193,789018236128391,29043982525257901,

%U 1147797409030815779,48471109094902530293,2178347851919531491093,103805969587115219167613,5228356786703601108008083

%N Largest prime with distinct digits when written in base n.

%C a(10) = 987654103 = A007810(9). For n >= 3, a(n) < A062813(n), a multiple of n.

%C Contribution R. J. Mathar, May 15 2010 (START):

%C Supposed all digits are used and the digits at positions 0 to n-1 are d_0, d_1,... d_{n-1}, the candidates are d_0+d_1*n+d_2*n^2+....+d_{n-1}*n^(n-1).

%C These values are (n-1)*n/2 (mod n-1), and they cannot be prime if n is even, because this number is = 0 (mod n-1) then, showing that n-1 is a divisor.

%C In conclusion, if n is even, the entries have at most n-1 digits in base n. (END)

%C If n is odd then the candidate numbers considered in the previous comment are divisible by (n-1)/2. Hence, we conclude that for n>3, a(n) has at most n-1 digits in base n. Conjecture: for n>3, a(n) has exactly n-1 digits in base n. - _Eric M. Schmidt_, Oct 26 2014

%H Eric M. Schmidt, <a href="/A132129/b132129.txt">Table of n, a(n) for n = 2..200</a>

%e a(9) = 42373937 as the prime 42373937 (base 10) = 87654102 (base 9), the largest prime number with distinct digits when represented in base 9.

%o (Sage) def a(n) :

%o     if n==2 : return 2

%o     if n==3 : return 19

%o     for P in Permutations(range(n-1,-1,-1), n-1) :

%o         N = sum(P[-1-i]*n^i for i in range(n-1))

%o         if is_prime(N) : return N

%o # _Eric M. Schmidt_, Oct 26 2014

%Y Cf. A062813, A007810, A029743.

%K base,nonn

%O 2,1

%A _Rick L. Shepherd_, Aug 11 2007

%E Removed my claim of finiteness of the sequence. - _R. J. Mathar_, May 18 2010

%E a(11)-a(20) from _Eric M. Schmidt_, Oct 26 2014