OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
Sum_{n>=1} 1/a(n) = (7*9)/((7-1)*(9-1)) = 21/16. - Amiram Eldar, Sep 24 2020
a(n) ~ exp(sqrt(2*log(7)*log(9)*n)) / sqrt(63). - Vaclav Kotesovec, Sep 24 2020
MATHEMATICA
With[{nn=40}, Take[Union[7^First[#] 9^Last[#]&/@Tuples[Range[0, nn/4], 2]], nn]] (* Harvey P. Dale, Mar 06 2014 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
STATUS
approved