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A355078
a(n) is the smallest number k with exactly n divisors in A033075.
0
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
1,2
EXAMPLE
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.
PROG
(Magma) alt:=func<n| forall{i:i in [1..#Intseq(n)-1]|Abs(Intseq(n)[i+1]-Intseq(n)[i]) eq 1}>; 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
CROSSREFS
Cf. A033075.
Sequence in context: A334390 A067993 A074131 * A335038 A019464 A064402
KEYWORD
nonn,base
AUTHOR
Marius A. Burtea, Jul 11 2022
STATUS
approved