A101932 - OEIS

A101932

Numbers n with omega(n) equal to omega(n-1) and omega (n+1).

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

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OFFSET

1,1

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..5000

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 A374311

Adjacent sequences: A101929 A101930 A101931 * A101933 A101934 A101935

KEYWORD

easy,nonn

AUTHOR

Neil Fernandez, Dec 21 2004

STATUS

approved