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A115165 Odd numbers k such that k-1 and k+1 have the same number of distinct prime divisors. 1
3, 11, 13, 19, 21, 23, 25, 27, 35, 37, 39, 45, 47, 49, 51, 53, 55, 57, 73, 75, 81, 87, 93, 95, 97, 99, 105, 107, 117, 123, 131, 135, 139, 143, 145, 147, 155, 159, 161, 163, 165, 169, 177, 181, 193, 195, 201, 207, 213, 215, 217, 221, 225, 229, 239, 243, 249, 259, 265 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

MATHEMATICA

Select[Range[1, 301, 2], PrimeNu[#-1] == PrimeNu[#+1]&] (* Jean-François Alcover, Oct 18 2016 *)

PROG

(PARI) g(n) = forstep(x=3, n, 2, p1=omega(x-1); p2=omega(x+1); if(p1==p2, print(x", ")))

(Magma) [k: k in [3..265 by 2]| #PrimeDivisors(k-1) eq #PrimeDivisors(k+1)]; // Marius A. Burtea, Feb 19 2020

CROSSREFS

Subsequence of A088070.

Cf. A001221.

Sequence in context: A158296 A160025 A045427 * A050583 A045428 A338445

Adjacent sequences: A115162 A115163 A115164 * A115166 A115167 A115168

KEYWORD

easy,nonn

AUTHOR

Cino Hilliard, Mar 03 2006

EXTENSIONS

Offset corrected by Michel Marcus, Oct 18 2016

STATUS

approved

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Last modified December 7 17:25 EST 2022. Contains 358668 sequences. (Running on oeis4.)