OFFSET
1,1
LINKS
Harry J. Smith, Table of n, a(n) for n=1,...,1000
EXAMPLE
C(39) = 15, C(39+3) = 2*15.
PROG
(PARI) C(n)=n-eulerphi(n); j=[]; for(n=1, 20000, if(C(n+3)==2*C(n), j=concat(j, n))); j
(PARI) { n=0; c1=c2=c3=1; for (m=1, 10^9, c=c1; c1=c2; c2=c3; c3=m-eulerphi(m); if (c3==2*c, write("b063480.txt", n++, " ", m - 3); if (n==1000, break)) ) } \\ Harry J. Smith, Aug 23 2009
CROSSREFS
KEYWORD
nonn
AUTHOR
Jason Earls, Jul 28 2001
STATUS
approved