OFFSET
1,4
COMMENTS
Sequence was suggested by the discovery that the digital root of A068943 is 9 for all n>3.
EXAMPLE
a(11)=23446 since f(11,11,11)=9^binomial(12,10) * 6^binomial(15,10) * 3^(18,10) * other terms. this implies a(11)=binomial(12,10) + 1/2*(binomial(15,10)-1 + binomial(18,10)).
CROSSREFS
KEYWORD
nonn
AUTHOR
Francois Jooste (phukraut(AT)hotmail.com), Mar 09 2002
STATUS
approved