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A175355 Noncomposite reverse concatenations of divisors of n, sorted by n.

%I A175355 #12 Aug 12 2020 14:37:04
%S A175355 1,31,421,71,131,191,2551,311,391331,431,48241612864321,911371,971,
%T A175355 1031,1091,1173913931,1511,1571,1811,1931,2111,2411,24412261421,
%U A175355 24719131,2711,289171,29214673421,3014371,30910331,32565251351,3371,3491,3671
%N A175355 Noncomposite reverse concatenations of divisors of n, sorted by n.
%H A175355 Robert Israel, <a href="/A175355/b175355.txt">Table of n, a(n) for n = 1..10000</a>
%F A175355 a(n) = A176558(A089374(n)).
%F A175355 a(n) = A069582(n-1), n>1. [_R. J. Mathar_, May 03 2010]
%e A175355 For n = 9; a(9) = 391331 because A089374(9) = 39 and divisors of 39 are 1, 3, 13, 39; reverse concatenation of divisors A176558(21) = 391331 is noncomposite.
%p A175355 rcd:= proc(n) local D,T,i;
%p A175355   D:= sort(convert(numtheory:-divisors(n),list));
%p A175355   T:= D[1];
%p A175355   for i from 2 to nops(D) do
%p A175355     T:= T + 10^(1+ilog10(T))*D[i]
%p A175355   od;
%p A175355   T
%p A175355 end proc:
%p A175355 select(t -> t=1 or isprime(t), map(rcd, [$1..1000])); # _Robert Israel_, Aug 12 2020
%Y A175355 Subsequence of A176558(n).  Supersequence of A055781.
%K A175355 nonn,base
%O A175355 1,2
%A A175355 _Jaroslav Krizek_, Apr 20 2010
%E A175355 Edited by _Charles R Greathouse IV_, Apr 30 2010