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

Author

Omar E. Pol, Aug 17 2021

Keywords

• nonn

Examples

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

Crossrefs

Cf. A002182, A018252, A068507, A346529.

Programs

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 *)

Extensions

More terms from Amiram Eldar, Aug 17 2021