A101938 Numbers n with omega(n) < omega of 2 nearest larger and 2 nearest smaller neighbors.

37, 53, 64, 67, 89, 97, 113, 121, 131, 157, 163, 173, 211, 223, 233, 251, 263, 277, 289, 293, 307, 317, 331, 337, 343, 353, 367, 373, 379, 383, 389, 397, 401, 409, 439, 443, 449, 457, 467, 479, 487, 491, 499, 503, 509, 512, 529, 541, 547

Offset

1,1

Links

G. C. Greubel, Table of n, a(n) for n = 1..10000

Example

173 is in the sequence because it has one unique prime factor (itself), whereas
171, 172, 174 and 175 each have more.

Mathematica

For[i=2, i<1000, If[And[Length[FactorInteger[i-2]]>Length[FactorInteger[i]], Length[FactorInteger[i-1]]>Length[FactorInteger[i]], Length[FactorInteger[i+1]]>Length[FactorInteger[i]], Length[FactorInteger[i+2]]>Length[FactorInteger[i]]], Print[i]]; i++ ]
Select[Range[6500], PrimeNu[#] < Min[PrimeNu[# - 1], PrimeNu[# - 2], PrimeNu[# + 1], PrimeNu[# + 2]] &] (* G. C. Greubel, May 15 2017 *)

Crossrefs

Cf. A001221, A101934.

Sequence in context: A345169 A350250 A092105 * A060330 A302720 A304358

Adjacent sequences: A101935 A101936 A101937 * A101939 A101940 A101941

Keyword

easy,nonn

Author

Neil Fernandez, Dec 21 2004

Status

approved