OFFSET
1,1
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..1000
EXAMPLE
8 = 3+5 = phi(3)*phi(5) = 2*4;
12 = 3+9 = phi(3)*phi(9) = 2*6;
24 = 3+21 = phi(3)*phi(21) = 2*12 or 24 = 10+14 = phi(10)*phi(14) = 4*6.
MAPLE
with(numtheory): P:=proc(q) local a, b, k, n; for n from 1 to q do
for k from 1 to trunc(n/2) do if phi(k)*phi(n-k)=n then print(n); break; fi;
od; od; end: P(10^9);
PROG
(PARI) is(n)=for(x=1, n\2, if(eulerphi(x)+eulerphi(n-x)==n, return(1))); 0 \\ Charles R Greathouse IV, Jun 07 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, May 31 2016
EXTENSIONS
a(19)-a(39) from Giovanni Resta, May 31 2016
STATUS
approved