OFFSET
1,1
COMMENTS
a(8) has 165 decimal digits and a(9) has 331 decimal digits. - Andrew Howroyd, Sep 09 2019
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..10
Eric Weisstein's World of Mathematics, Apollonian Network
Eric Weisstein's World of Mathematics, Graph Cycle
PROG
(PARI)
P(c, d)={[2*d^3 + 7*d^2 + (6*c + 2)*d + 2*c, 3*d^2 + 5*d + (c + 1)]}
R(c, d)={16*d^3 + (9*c + 51)*d^2 + (30*c + 27)*d + (3*c^2 + 9*c + 4)}
a(n)={my(s=1, c=0, d=0); for(i=1, n, s = 3*s + R(c, d); [c, d]=P(c, d)); s} \\ Andrew Howroyd, Sep 10 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Apr 14 2018
EXTENSIONS
a(5)-a(7) from Andrew Howroyd, Sep 09 2019
STATUS
approved