OFFSET
1,1
COMMENTS
The next term (a(8)) has 924 digits. - Harvey P. Dale, Feb 06 2014
REFERENCES
John Derbyshire, Prime Obsession, Joseph Henry Press, April 2004, p. 16.
FORMULA
Given a(0)=1, b(0)=1 then for i=1, 2, .. a(i)/b(i) = (a(i-1)+2*b(i-1)) /(a(i-1) + b(i-1)).
MATHEMATICA
nxt[{t_, b_}]:={t+10b, t+b}; Select[Transpose[NestList[nxt, {1, 1}, 60]][[2]], PrimeQ] (* Harvey P. Dale, Feb 06 2014 *)
PROG
(PARI) primenum(n, k, typ) = \ k=mult, typ=1 num, 2 denom. output prime num or denom. { local(a, b, x, tmp, v); a=1; b=1; for(x=1, n, tmp=b; b=a+b; a=k*tmp+a; if(typ==1, v=a, v=b); if(isprime(v), print1(v", "); ) ); print(); print(a/b+.) }
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, Oct 02 2005
EXTENSIONS
Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, May 16 2007
One more term (a(7)) from Harvey P. Dale, Feb 06 2014
STATUS
approved