A249301 Composite numbers whose concatenation of their aliquot parts, in descending order, is a palindrome.

39, 119, 121, 169, 254, 289, 361, 393, 411, 417, 755, 785, 1211, 1253, 1703, 2554, 3503, 3629, 4197, 6401, 7555, 10001, 12131, 12287, 12439, 14803, 15563, 17147, 17363, 23701, 24202, 24322, 24646, 24686, 24746, 25514, 25838, 25918, 25958, 26827, 30383, 30521

Offset: 1

Author

Paolo P. Lava, Oct 24 2014

Keywords

• nonn
• base

Examples

			Aliquot parts of 24332 are 1, 2, 121661; their concatenation in descending order is concat(12166,2,1) = 1216621, which is a palindrome.
		

Links

• Paolo P. Lava, Table of n, a(n) for n = 1..100

Crossrefs

Cf. A046449.

Programs

Maple

with(numtheory): P:=proc(q) local a,b,c,k,n;
for n from 2 to q do if not isprime(n) then a:=sort([op(divisors(n))]); b:=0;
for k from 1 to nops(a)-1 do b:=b*10^(ilog10(a[k])+1)+a[k]; od; a:=0; c:=b;
for k from 1 to ilog10(b)+1 do a:=10*a+(c mod 10); c:=trunc(c/10); od;
if a=b then print(n); fi; fi; od; end: P(10^9);

PARI

isok(n) = {d = vecsort(divisors(n),,4); if (#d > 2, s = ""; for (i=2, #d, s = concat(s, Str(d[i]));); d = digits(eval(s)); d == Vecrev(d););} \\ Michel Marcus, Oct 25 2014