login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A101932 Numbers n with omega(n) equal to omega(n-1) and omega (n+1). 6
3, 4, 8, 21, 34, 35, 39, 45, 51, 55, 56, 57, 75, 76, 86, 87, 92, 93, 94, 95, 99, 116, 117, 118, 123, 134, 135, 142, 143, 144, 145, 146, 147, 159, 160, 161, 176, 177, 184, 188, 201, 202, 206, 207, 208, 213, 214, 215, 216, 217, 218, 225 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
45 is in the sequence because it has 2 prime factors (3 and 5) as do 44 (2 and 11) and 46 (2 and 23).
MATHEMATICA
For[i=1, i<1000, If[And[Length[FactorInteger[i-1]]==Length[FactorInteger[i]], Length[FactorInteger[i+1]]==Length[FactorInteger[i]]], Print[i]]; i++ ]
Select[Range[2, 225], PrimeNu[#] == PrimeNu[# - 1] == PrimeNu[# + 1] &] (* Jayanta Basu, Aug 11 2013 *)
SequencePosition[PrimeNu[Range[300]], {x_, x_, x_}][[All, 1]]+1 (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 18 2018 *)
PROG
(PARI) isok(n) = (omega(n) == omega(n-1)) && (omega(n)==omega(n+1)) \\ Michel Marcus, May 05 2017
CROSSREFS
Cf. A001221.
Subsequence of A006049.
Sequence in context: A332707 A129285 A051440 * A204521 A073313 A217248
KEYWORD
easy,nonn
AUTHOR
Neil Fernandez, Dec 21 2004
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 29 10:22 EDT 2024. Contains 371268 sequences. (Running on oeis4.)