A139208 Numbers 2*k+1 for which numbers A006694(k) are record values for A006694.

1, 3, 7, 15, 21, 31, 45, 63, 93, 105, 127, 189, 217, 255, 315, 341, 455, 511, 819, 1023, 1365, 2047, 3591, 3855, 4095, 5461, 8191, 12483, 13107, 16383, 21845, 29127, 32767, 53261, 55831, 60787, 65535, 87381, 131071, 178481, 182361, 209715, 258111, 262143, 349525, 430185, 479349, 524287

Offset: 1

Author

Vladimir Shevelev, Jun 06 2008

Keywords

• nonn

Comments

Question. Is it true that all primes in this sequence are Mersenne primes?

178481 is a prime term, but is not a Mersenne prime. - Michel Marcus, Dec 18 2018

Crossrefs

Cf. A006694, A000668.

Programs

PARI

a006694(n)=sumdiv(2*n+1, d, eulerphi(d)/znorder(Mod(2, d))) - 1;
lista(nn) = {my(m = -1, newm); for(n=0, nn, newm = a006694(n); if (newm > m, m = newm; print1(2*n+1, ", ")););} \\ Michel Marcus, Dec 18 2018

Extensions

Offset 1, missing term 819 and more terms from Michel Marcus, Dec 18 2018