A355078 a(n) is the smallest number k with exactly n divisors in A033075.

1, 2, 4, 6, 18, 12, 24, 60, 120, 168, 360, 1080, 840, 3360, 2520, 7560, 15120, 30240, 84840, 196560, 339360, 254520, 1102920, 763560, 1527120, 4581360, 3054240, 9162720, 9926280, 19852560, 59557680, 39705120, 119115360, 277935840, 674987040, 1151448480, 1469089440

Offset: 1

Author

Marius A. Burtea, Jul 11 2022

Keywords

• nonn
• base

Examples

			1 has a single divisor in A033075, so a(1) = 1.
2 has divisors 1 and 2 in A033075, so a(2) = 2;
3 has only divisors 1, 3 in A033075, 4 has divisors 1, 2, 4 in A033075, so a(3) = 4.
5 has only divisors 1, 5 in A033075, 6 has divisors 1, 2, 3, 6 in A033075, so a(4) = 6.
		

Crossrefs

Cf. A033075.

Programs

Magma

alt:=func; a:=[]; for n in [1..37] do k:=1; while #[d:d in Divisors(k)|alt(d)] ne n do k:=k+1; end while; Append(~a,k); end for; a;

PARI

diff(v)=vector(#v-1, i, v[i+1]-v[i]);
is(n)=if(n>9, Set(abs(diff(digits(n))))==[1], n>0);
a(n) = my(k=1); while (sumdiv(k, d, is(d)) != n, k++); k; \\ Michel Marcus, Jul 11 2022