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A117360 Numbers m such that m and 2*m+1 have the same number of prime factors. 3
2, 3, 4, 5, 10, 11, 23, 25, 29, 34, 38, 40, 41, 46, 52, 53, 55, 57, 76, 77, 83, 89, 91, 93, 106, 113, 118, 123, 129, 130, 131, 133, 143, 145, 159, 161, 169, 171, 172, 173, 177, 179, 185, 191, 201, 203, 205, 206, 212, 213, 218, 220, 226, 233, 235, 238, 239, 251 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A001222(a(n)) = A001222(2*a(n)+1);

Sophie Germain primes are a subsequence, see A005384.

LINKS

R. Zumkeller, Table of n, a(n) for n = 1..10000

EXAMPLE

m=52=2*2*13, 2*52+1=105=3*5*7, therefore 52 is a term.

MATHEMATICA

Select[Range[255], PrimeOmega[#] == PrimeOmega[2 # + 1] &] (* Ivan Neretin, Apr 30 2016 *)

PROG

(PARI) is(n)=bigomega(n)==bigomega(2*n+1) \\ Charles R Greathouse IV, Apr 30 2016

CROSSREFS

Cf. A068406.

Sequence in context: A023787 A032983 A204388 * A074821 A296160 A076707

Adjacent sequences:  A117357 A117358 A117359 * A117361 A117362 A117363

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Mar 10 2006

STATUS

approved

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Last modified November 14 02:19 EST 2019. Contains 329108 sequences. (Running on oeis4.)