OFFSET
1,1
COMMENTS
If k = p^2 is the square of a prime, then p^2 - phi(p^2) = p, so this sequence is infinite and generates all primes.
No prime p is a term of this sequence because A051953(p)=1. Other cases exist; e.g., k - phi(k) = 23 if k = 95, 119, 143, 529.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
Numbers k such that A051953(k) is prime.
MATHEMATICA
Select[Range[600], PrimeQ[#-EulerPhi[#]]&] (* Harvey P. Dale, Jun 23 2013 *)
PROG
(Magma) [n: n in [1..600] | IsPrime(n-EulerPhi(n))]; // Vincenzo Librandi, Dec 18 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 29 1999
STATUS
approved