A001770 Numbers k such that 5*2^k - 1 is prime.
2, 4, 8, 10, 12, 14, 18, 32, 48, 54, 72, 148, 184, 248, 270, 274, 420, 1340, 1438, 1522, 1638, 1754, 1884, 2014, 2170, 2548, 2622, 2652, 2704, 13510, 21738, 25624, 41934, 51478, 52540, 53230, 172300, 245728, 350028, 1194164
Offset: 1
References
- N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
- N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
Links
- Y. Gallot, Proth.exe: Windows Program for Finding Large Primes
- Wilfrid Keller, List of primes k.2^n - 1 for k < 300
- H. C. Williams and C. R. Zarnke, A report on prime numbers of the forms M = (6a+1)*2^(2m-1)-1 and (6a-1)*2^(2m)-1, Math. Comp., 22 (1968), 420-422.
- Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime
Programs
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Maple
A001770:=n->`if`(isprime(5*2^n-1),n,NULL): seq(A001770(n), n=1..1000); # Wesley Ivan Hurt, Oct 15 2014
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Mathematica
Select[Range[1000], PrimeQ[5*2^# - 1] &] (* Vaclav Kotesovec, Apr 28 2014 *)
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PARI
is(n)=isprime(5*2^n-1) \\ Charles R Greathouse IV, Feb 07 2017
Extensions
More terms from Hugo Pfoertner, Jun 23 2004
a(40) from the Wilfrid Keller link by Robert Price, Dec 22 2018
Comments