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A139208 Numbers 2*k+1 for which numbers A006694(k) are record values for A006694. 0
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 (list; graph; refs; listen; history; text; internal format)
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: A182247 A121712 A175544 * 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

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Last modified May 28 12:18 EDT 2020. Contains 334681 sequences. (Running on oeis4.)