A124477 Numbers k such that 24k+7 is a Mersenne prime (A000668).

0, 1, 5, 341, 5461, 21845, 89478485, 96076792050570581, 25790417485112089060398421, 6760803201217223474649083762005, 7089215977519551322153637654828504405

Offset: 1

Author

Artur Jasinski, Dec 17 2006

Keywords

• nonn

Comments

Note that 2^m - 1 can be expressed as 24*k+7 whenever m is an odd integer >= 3. - Robert Israel, Jul 08 2014

Links

• Michel Marcus, Table of n, a(n) for n = 1..18

Crossrefs

Cf. A000043, A000668, A139480.

Programs

Maple

seq((numtheory:-mersenne([i+1])-7)/24, i=1..20); # Robert Israel, Jul 08 2014

PARI

for(n=0, 1e20, k=0; if(ispseudoprime(24*n+7), while(2^k-1 < 24*n+7, k++); if(24*n+7==2^k-1, print1(n, ", ")))) \\ Felix Fröhlich, Jul 04 2014

PARI

lista(nn) = {vmps = readvec("b000043.txt"); if (nn== 0, nn = #vmps); for (i=1, nn, mpi = 2^vmps[i]-8; if ((mpi % 24) == 0, print1(mpi/24, ", ")););} \\ Michel Marcus, Jul 05 2014

Formula

a(n) = (2^A000043(n+1)-8)/24. - Jeppe Stig Nielsen, Sep 17 2020

Extensions

a(11) corrected by Michel Marcus, Jul 05 2014