This site is supported by donations to The OEIS Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A061644 "Right perfect numbers": primes of the form 1 + a perfect number. 4
 7, 29, 33550337, 137438691329 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Readers of Rivera's web page (which I believe was indirectly based on this entry) later showed that there are no more cases among the first 39 perfect numbers. - N. J. A. Sloane, May 25 2004. The latest news is that there are no more cases among the first 44 perfect numbers. - M. F. Hasler, Jun 05 2008 So of the 44 known perfect numbers P=2^(p-1)*(2^p-1), P+1 is only prime for p=2,3,13 and 19. If p is in the sequence then for each positive integer k, p^k is a solution to the equation sigma(phi(x)) = 2x-2. Proof: take t=2 in theorem related to the sequence A093034. [M. F. Hasler and Farideh Firoozbakht, Sep 09 2014] LINKS Mersenne Forum, Thread 10336 C. Rivera, Puzzle 203 FORMULA P(p)*[P(p)+1]/2 + 1 is prime, where P(p) is a Mersenne prime. (corrected by Lekraj Beedassy, May 01 2009) MATHEMATICA pn={6, 28, 496, 8128, 33550336, 8589869056, 137438691328, 2305843008139952128, 2658455991569831744654692615953842176, 191561942608236107294793378084303638130997321548169216}; lst={}; Do[p=pn[[n]]+1; If[PrimeQ[p], AppendTo[lst, p]], {n, Length[pn]}]; lst... and/or...PerfectNum[n_]:=Plus@@Divisors[n]/2; lst={}; Do[p=PerfectNum[n]; If[p==n&&PrimeQ[p+1], AppendTo[lst, p+1]], {n, 10!}]; lst (* Vladimir Joseph Stephan Orlovsky, Jan 27 2009 *) PROG (PARI) forprime(p=2, 100, P=2^p-1; Q=P*(P+1)/2+1; if(isprime(P)&&isprime(Q), print1(Q, ", "))) \\ Edward Jiang, Sep 10 2014 CROSSREFS Cf. A000396. Analogous right and left multiple perfect numbers are in A093034, A094467. Sequence in context: A122119 A300528 A157422 * A053621 A210107 A266604 Adjacent sequences:  A061641 A061642 A061643 * A061645 A061646 A061647 KEYWORD more,nonn AUTHOR Labos Elemer, Jun 14 2001 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 24 17:09 EDT 2019. Contains 323533 sequences. (Running on oeis4.)