login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A268175 Smallest number k such that k*(2^(2*A000043(n))-1)+1 is prime. 0
2, 2, 4, 6, 12, 82, 14, 22, 244, 44, 120, 94, 1010, 764, 834, 1076, 516, 3252, 1384, 1664, 7040, 6104, 20942, 14344, 37142, 12522, 12554, 64160, 32172, 44460, 49400, 291726 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The numbers k*(2^(2*A000043(n))-1)+1 may be written as k*(2^A000043(n)-1)*(2^A000043(n)+1)+1 or k*Mersenne(n)*(Mersenne(n)+2)+1 and so may be proved primes.

All the numbers a(n)*(2^(2*A000043(n)-1)+1 for n=1 to 32 have been proved to be primes.

LINKS

Table of n, a(n) for n=1..32.

EXAMPLE

2*(2^(2*2)-1)+1 = 31 (prime) and A000043(1) = 2, so a(1) = 2.

2*(2^(2*3)-1)+1 = 127 (prime) and A000043(2) = 3, so a(2) = 2.

MATHEMATICA

A000043 = {2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127, 521, 607, 1279, 2203, 2281, 3217, 4253, 4423, 9689, 9941, 11213, 19937, 21701, 23209, 44497, 86243, 110503, 132049, 216091, 756839, 859433, 1257787, 1398269, 2976221, 3021377, 6972593, 13466917, 20996011, 24036583, 25964951, 30402457, 32582657};

lst = {}; maxk = 5000; maxn = 15;

For[n = 1, n ≤ maxn, n++,

  For[k = 0, k ≤ maxk, k++,

    If[PrimeQ[k*(2^(2*A000043[[n]]) - 1) + 1], AppendTo[lst, k]; Break[]]

  ]

];

lst (* Robert Price, Apr 05 2016 *)

CROSSREFS

Cf. A000043.

Sequence in context: A274935 A188538 A282164 * A209025 A153955 A074028

Adjacent sequences:  A268172 A268173 A268174 * A268176 A268177 A268178

KEYWORD

nonn,more

AUTHOR

Pierre CAMI, Jan 28 2016

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 18 10:19 EDT 2021. Contains 343995 sequences. (Running on oeis4.)