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A176558 a(n) is the reverse concatenation of divisors of n.

%I A176558 #33 Dec 31 2020 09:33:16
%S A176558 1,21,31,421,51,6321,71,8421,931,10521,111,1264321,131,14721,15531,
%T A176558 168421,171,1896321,191,20105421,21731,221121,231,2412864321,2551,
%U A176558 261321,27931,28147421,291,30151065321,311,32168421,331131,341721,35751,361812964321,371
%N A176558 a(n) is the reverse concatenation of divisors of n.
%C A176558 Union of A089374(n) for n >= 1 and A175354(n) for n >= 2. - _Jonathan Vos Post_, Apr 17 2011
%H A176558 Indranil Ghosh, <a href="/A176558/b176558.txt">Table of n, a(n) for n = 1..50000</a>
%e A176558 For n=12; divisors of 12: 1,2,3,4,6,12; a(12)=1264321 (reverse concatenation).
%p A176558 a:= n-> parse(cat(sort([numtheory[divisors](n)[]], `>`)[])):
%p A176558 seq(a(n), n=0..40);  # _Alois P. Heinz_, Dec 31 2020
%t A176558 Table[FromDigits@ Flatten@ Map[IntegerDigits, Reverse@ Divisors@ n], {n, 34}] (* _Michael De Vlieger_, Jan 23 2017 *)
%o A176558 (PARI) a(n) = {s = ""; fordiv(n, d, s = concat(Str(d), s)); eval(s);} \\ _Michel Marcus_, Feb 16 2015
%o A176558 (Python)
%o A176558 from sympy import divisors
%o A176558 def a(n): return int("".join(str(d) for d in divisors(n)[::-1]))
%o A176558 print([a(n) for n in range(1, 35)]) # _Michael S. Branicky_, Dec 31 2020
%Y A176558 Cf. A089374, A175354, A175355, A176588, A176589.
%K A176558 nonn,base
%O A176558 1,2
%A A176558 _Jaroslav Krizek_, Apr 20 2010
%E A176558 More terms from _Charles R Greathouse IV_, Apr 23 2010
%E A176558 Corrected by _Jaroslav Krizek_, Apr 26 2010
%E A176558 Edited by _Charles R Greathouse IV_, Apr 30 2010