OFFSET
1,1
REFERENCES
R. K. Guy, Unsolved Problems Number Theory, B37.
LINKS
C. Rivera, Puzzle 76
M. V. Subbarao, On two congruences for primality, Pacific Journal of Mathematics, 52 (1974), 261-268. (PDF)
MATHEMATICA
Select[Range[2, 250], Mod[#*DivisorSigma[1, #]-2, EulerPhi[#]]==0&] (* Harvey P. Dale, Sep 22 2021 *)
PROG
(PARI) a(n)=if(n<12, [2, 3, 4, 5, 6, 7, 11, 13, 17, 19, 22][n], prime(n-3)) \\ Charles R Greathouse IV, Aug 26 2011
CROSSREFS
KEYWORD
nonn,nice,easy
AUTHOR
N. J. A. Sloane, Dec 21 1999
STATUS
approved