OFFSET
1,1
COMMENTS
Venkataraman showed that, for every p of this form, 3p is a perfect totient number (cf. A082897).
REFERENCES
T. Venkataraman, Perfect totient number, The Mathematics Student, Vol. 43 (1975), p. 178. MR0447089.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..14
Paul Loomis, Michael Plytage and John Polhill, Summing up the Euler phi function, The College Mathematics Journal, Vol. 39, No. 1 (Jan. 2008), pp. 34-42 (see Corollary 3).
FORMULA
4*3^k + 1 where k belongs to A005537.
EXAMPLE
37 = 4*3^2 + 1 is a prime of this form. 973 = 4*3^5 + 1 = 7*139 is not a prime, so is not included in this sequence.
MATHEMATICA
Do[p = 4*3^i + 1; If[PrimeQ@p, Print@p], {i, 0, 300}] (* Robert G. Wilson v, Feb 20 2007 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
David Eppstein, Feb 06 2007, Feb 07 2007
EXTENSIONS
2 more terms from Robert G. Wilson v, Feb 20 2007
STATUS
approved