A176589 -id:A176589 - cp's OEIS frontend

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

1, 21, 31, 421, 51, 6321, 71, 8421, 931, 10521, 111, 1264321, 131, 14721, 15531, 168421, 171, 1896321, 191, 20105421, 21731, 221121, 231, 2412864321, 2551, 261321, 27931, 28147421, 291, 30151065321, 311, 32168421, 331131, 341721, 35751, 361812964321, 371

Offset: 1

Jaroslav Krizek, Apr 20 2010

Union of A089374(n) for n >= 1 and A175354(n) for n >= 2. - Jonathan Vos Post, Apr 17 2011

			For n=12; divisors of 12: 1,2,3,4,6,12; a(12)=1264321 (reverse concatenation).

Indranil Ghosh, Table of n, a(n) for n = 1..50000

Cf. A089374, A175354, A175355, A176588, A176589.

a:= n-> parse(cat(sort([numtheory[divisors](n)[]], `>`)[])):
seq(a(n), n=0..40);  # Alois P. Heinz, Dec 31 2020

Table[FromDigits@ Flatten@ Map[IntegerDigits, Reverse@ Divisors@ n], {n, 34}] (* Michael De Vlieger, Jan 23 2017 *)

a(n) = {s = ""; fordiv(n, d, s = concat(Str(d), s)); eval(s);} \\ Michel Marcus, Feb 16 2015

from sympy import divisors
def a(n): return int("".join(str(d) for d in divisors(n)[::-1]))
print([a(n) for n in range(1, 35)]) # Michael S. Branicky, Dec 31 2020

More terms from Charles R Greathouse IV, Apr 23 2010
Corrected by Jaroslav Krizek, Apr 26 2010
Edited by Charles R Greathouse IV, Apr 30 2010

A176590 Numbers k such that both concatenation of divisors of k and reverse concatenation of divisors of k are nonprime.

Original entry on oeis.org

1, 2, 5, 6, 8, 10, 11, 12, 14, 15, 16, 17, 18, 20, 22, 23, 24, 26, 27, 28, 29, 30, 32, 33, 34, 35, 36, 38, 40, 41, 42, 44, 45, 46, 47, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 68, 69, 70, 71, 72, 74, 75, 76, 77, 78, 80, 81, 82, 83, 84, 85, 86, 87, 88

Offset: 1

Jaroslav Krizek, Apr 21 2010

Numbers k such that both A037278(k) and A176558(k) are nonprime.

			10 is a term; divisors of 10: 1, 2, 5, 10; both concatenation of divisors 12510 and reverse concatenation of divisors 10521 are nonprime numbers.
Sequence of corresponding values of concatenations of divisors of a(n): 1, 12, 15, 1236, 1248, 12510, 111, ...
Sequence of corresponding values of reverse concatenations of divisors of a(n): 1, 21, 51, 6321, 8421, 10521, 111, ...

Cf. A037278, A176558, A176554, A175354, A176589.

Intersection of A176554 and A175354. - Jason Yuen, Feb 08 2025

Extended and revised by Charles R Greathouse IV, Apr 24 2010

cp's OEIS Frontend

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

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