A340580 Ramanujan's highly composite numbers A002182 sandwiched between nonprimes.

120, 1680, 25200, 27720, 50400, 83160, 221760, 277200, 554400, 720720, 2162160, 2882880, 3603600, 7207200, 8648640, 10810800, 17297280, 21621600, 36756720, 73513440, 122522400, 147026880, 245044800, 294053760, 551350800, 2095133040, 2327925600, 2793510720, 3491888400

Offset

1,1

Links

Table of n, a(n) for n=1..29.

Example

120 is in the sequence because it is an highly composite numbers A002182 and its nearest neighbors 119 and 121 both are nonprimes.

Mathematica

s = {}; dm = 0; Do[d = DivisorSigma[0, n]; If[d > dm, dm = d; If[! PrimeQ[n - 1] && ! PrimeQ[n + 1], AppendTo[s, n]]], {n, 1, 10^6}]; s (* Amiram Eldar, Aug 17 2021 *)

Crossrefs

Cf. A002182, A018252, A068507, A346529.

Sequence in context: A027795 A223427 A282899 * A053567 A056270 A001118

Adjacent sequences: A340577 A340578 A340579 * A340581 A340582 A340583

Keyword

nonn

Author

Omar E. Pol, Aug 17 2021

Extensions

More terms from Amiram Eldar, Aug 17 2021

Status

approved