cp's OEIS Frontend

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.

%I A361320 #9 Mar 10 2023 19:38:33
%S A361320 1,2,3,2,5,23,7,24,3,25,11,2346,13,27,35,248,17,2369,19,24501,37,211,
%T A361320 23,2346821,5,231,39,24741,29,23560151,31,24861,311,271,57,234692181,
%U A361320 37,291,331,24580102,41,23674112,43,241122,35951,232,47,23468216142,7,250152
%N 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.
%C A361320 First differs from A037279 at a(20).
%e A361320 Divisors of 20 are 1,2,4,5,10,20, so a(20)=24501.
%o A361320 (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
%Y A361320 Cf. A037279, A130140.
%K A361320 nonn,base
%O A361320 1,2
%A A361320 _Tyler Busby_, Mar 09 2023