The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A123674

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A123674

a(n) = number of primes of the form 2^n - 3^k.
(history; published version)

#5 by Alois P. Heinz at Wed Oct 18 14:19:51 EDT 2017

STATUS

proposed

approved

#4 by G. C. Greubel at Wed Oct 18 14:16:37 EDT 2017

STATUS

editing

proposed

#3 by G. C. Greubel at Wed Oct 18 14:16:16 EDT 2017

LINKS

G. C. Greubel, <a href="/A123674/b123674.txt">Table of n, a(n) for n = 1..1000</a>

STATUS

approved

editing

#2 by Russ Cox at Sat Mar 31 13:20:33 EDT 2012

AUTHOR

_Alexander Adamchuk (alex(AT)kolmogorov.com), _, Nov 17 2006

Discussion

Sat Mar 31

13:20

OEIS Server: https://oeis.org/edit/global/879

#1 by N. J. A. Sloane at Wed Dec 06 03:00:00 EST 2006

NAME

a(n) = number of primes of the form 2^n - 3^k.

DATA

0, 1, 2, 2, 4, 2, 3, 2, 4, 2, 2, 2, 3, 3, 1, 2, 4, 0, 3, 4, 4, 3, 3, 3, 0, 1, 1, 0, 2, 1, 1, 1, 3, 2, 3, 2, 2, 0, 1, 2, 2, 3, 0, 0, 4, 4, 3, 2, 5, 4, 4, 0, 0, 0, 1, 1, 4, 5, 2, 4, 3, 3, 0, 1, 1, 2, 5, 0, 1, 1, 4, 3, 1, 0, 1, 1, 3, 2, 3, 0, 2, 4, 2, 1, 2, 2, 3, 0, 7, 2, 4, 4, 2, 2, 2, 3, 5, 0, 3, 1, 1, 1, 3, 3, 2

OFFSET

1,3

COMMENTS

a(1) = 0 because there are no prime numbers of the form 2^1 - 3^k. a(2) = 1 because the only prime of the form 2^2 - 3^k is 2^2 - 3^0 = 3. a(3) = because there are two primes of the form 2^3 - 3^k: 2^3 - 3^0 = 7 and 2^3 - 3^1 = 5.

MATHEMATICA

Table[Length[Select[Range[0, Floor[Log[3, 2^n]]], PrimeQ[2^n-3^# ]&]], {n, 1, 200}]

KEYWORD

nonn,new

AUTHOR

Alexander Adamchuk (alex(AT)kolmogorov.com), Nov 17 2006

STATUS

approved