A361320 If n is composite, replace n with the concatenation of its nontrivial divisors, written in increasing order, each divisor being written in base 10 with its digits in reverse order, otherwise a(n) = n.

1, 2, 3, 2, 5, 23, 7, 24, 3, 25, 11, 2346, 13, 27, 35, 248, 17, 2369, 19, 24501, 37, 211, 23, 2346821, 5, 231, 39, 24741, 29, 23560151, 31, 24861, 311, 271, 57, 234692181, 37, 291, 331, 24580102, 41, 23674112, 43, 241122, 35951, 232, 47, 23468216142, 7, 250152

Offset

1,2

Comments

First differs from A037279 at a(20).

Links

Table of n, a(n) for n=1..50.

Example

Divisors of 20 are 1,2,4,5,10,20, so a(20)=24501.

Prog

(PARI) a(n) = if (isprime(n) || (n==1), return (n)); my(d=divisors(n), list=List()); for (i=2, #d-1, my(dd=digits(d[i])); forstep (j=#dd, 1, -1, listput(list, dd[j]))); fromdigits(Vec(list)); \\ Michel Marcus, Mar 09 2023

Crossrefs

Cf. A037279, A130140.

Sequence in context: A120716 A084318 A084317 * A037279 A163591 A085307

Adjacent sequences: A361317 A361318 A361319 * A361321 A361322 A361323

Keyword

nonn,base

Author

Tyler Busby, Mar 09 2023

Status

approved