RE New sequence

[Tautócrona]

And subsequently I've sent the logical companion sequence, the "proth-" primes:

3,7,11,23,31,47,79,127,191,223,239,383,479,607,863,991,1087,1151,1279,1471,1663,2111,2239,2687,2879,3391,3583,3967,5119,5503,6143,6271,6911,7039,8191,8447,8831,9343,10111,11519,11903,12671,12799,13183,13567,14207,14591,15359,16127,20479,21247
%N A000001 Prime numbers of the form k*2^n-1 with k<2^n ("Proth-" primes)
%C A000001 These numbers are analogous to proth primes, but substracting 1 instead of 
adding it.
%H A000001 <a href="http://mathworld.wolfram.com/ProthPrime.html"></a>
%e A000001 a(1)=3 because 3=1*2^2-1, and it's the first prime of this form.
%o A000001 (PARI) for(n=2,8,for(k=2^(n-2)+1,2^n,M=k*2^n-1;if(isprime(M),print1(M","),0)))

Note that the first term ( 3 ) isn't computed.


Jose