A350424 Numbers for which the number of their semiprime divisors sets a new record.

4, 12, 30, 60, 180, 210, 420, 1260, 2310, 4620, 13860, 30030, 60060, 180180, 510510, 1021020, 3063060, 9699690, 19399380, 58198140, 223092870, 446185740, 1338557220, 6469693230, 12939386460, 38818159380, 194090796900, 200560490130, 401120980260, 1203362940780, 6016814703900

Offset

1,1

Comments

Aside from the first term a(1)=4, the sequence appears to be a subset of A129912. - Bill McEachen, Dec 31 2021

Links

Table of n, a(n) for n=1..31.

Mathematica

nspd[n_]:=Count[Divisors[n], _?(PrimeOmega[#]==2&)]; DeleteDuplicates[Table[{n, nspd[n]}, {n, 194*10^5}], GreaterEqual[#1[[2]], #2[[2]]]&][[;; , 1]] (* The program generates the first 19 terms of the sequence. *) (* Harvey P. Dale, Dec 03 2024 *)

Crossrefs

A350425 gives the corresponding number of semiprime divisors.

Cf. A129912, A220264.

Sequence in context: A011938 A047177 A048077 * A220264 A367097 A212519

Adjacent sequences: A350421 A350422 A350423 * A350425 A350426 A350427

Keyword

nonn

Author

Hugo Pfoertner, Dec 30 2021

Status

approved