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

1,2

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

Links

Table of n, a(n) for n=1..48.

Prog

(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

Crossrefs

Cf. A006694, A000668.

Sequence in context: A121712 A175544 A373941 * A324727 A320026 A146435

Adjacent sequences: A139205 A139206 A139207 * A139209 A139210 A139211

Keyword

nonn

Author

Vladimir Shevelev, Jun 06 2008

Extensions

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

Status

approved