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A115166 Even numbers k such that k-2 and k+2 have the same number of distinct prime factors. 1
6, 8, 12, 16, 20, 22, 24, 26, 36, 38, 42, 46, 48, 50, 52, 54, 56, 60, 68, 70, 74, 78, 84, 90, 94, 96, 98, 102, 106, 110, 112, 114, 120, 128, 144, 146, 150, 152, 160, 162, 164, 172, 174, 184, 186, 188, 190, 194, 198, 204, 210, 214, 216, 232, 234, 236, 246, 252, 262 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

EXAMPLE

38 is in the sequence because 36 = 2^2 * 3^2 and 40 = 2^3 * 5.

MAPLE

with(numtheory): a:=proc(n) if nops(factorset(n-2))=nops(factorset(n+2)) then n else fi end: seq(a(2*n), n=2..133); # Emeric Deutsch, Mar 12 2006

MATHEMATICA

Select[Range[2, 262, 2], PrimeNu[# - 2] == PrimeNu[# + 2] &] (* Amiram Eldar, Feb 18 2020 *)

PROG

(PARI) g(n) = forstep(x=4, n, 2, p1=omega(x-2); p2=omega(x+2); if(p1==p2, print(x", ")))

(MAGMA) [k:k in [4.. 270 by 2]| #PrimeDivisors(k-2) eq #PrimeDivisors(k+2)]; // Marius A. Burtea, Feb 18 2020

CROSSREFS

Cf. A001221.

Subsequence of A005843.

Sequence in context: A177085 A338370 A194409 * A050992 A090259 A089241

Adjacent sequences:  A115163 A115164 A115165 * A115167 A115168 A115169

KEYWORD

easy,nonn

AUTHOR

Cino Hilliard, Mar 03 2006

STATUS

approved

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Last modified August 9 15:33 EDT 2022. Contains 356026 sequences. (Running on oeis4.)