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A115167 Odd numbers k such that k-1 and k+1 have the same number of prime divisors with multiplicity. 2
5, 19, 29, 43, 51, 55, 67, 69, 77, 89, 115, 151, 171, 173, 187, 189, 197, 233, 237, 243, 245, 249, 267, 271, 283, 285, 291, 295, 307, 317, 329, 341, 343, 349, 355, 403, 405, 411, 427, 429, 435, 437, 461, 489, 491, 507, 569, 571, 593, 597, 603, 605, 653, 665 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

MATHEMATICA

s = {}; o1 = 0; Do[o2 = PrimeOmega[n]; If[o1 == o2, AppendTo[s, n-1]]; o1 = o2, {n, 2, 666, 2}]; s (* Amiram Eldar, Sep 23 2019 *)

PROG

(PARI) g(n) = forstep(x=3, n, 2, p1=bigomega(x-1); p2=bigomega(x+1); if(p1==p2, print1(x", ")))

(Python)

from sympy import primeomega

def aupto(limit):

  prv, nxt, alst = 1, 2, []

  for n in range(3, limit+1, 2):

    if prv == nxt: alst.append(n)

    prv, nxt = nxt, primeomega(n+3)

  return alst

print(aupto(665)) # Michael S. Branicky, May 19 2021

CROSSREFS

Subsequence of A280382.

Sequence in context: A251623 A341079 A045456 * A115103 A241043 A045457

Adjacent sequences:  A115164 A115165 A115166 * A115168 A115169 A115170

KEYWORD

easy,nonn

AUTHOR

Cino Hilliard, Mar 03 2006

STATUS

approved

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Last modified August 10 10:09 EDT 2022. Contains 356039 sequences. (Running on oeis4.)