OFFSET
1,3
COMMENTS
a(n) is the number of n-digit numbers in A348054.
FORMULA
a(n) < A052268(n).
Conjecture: lim_{n->infinity} a(n)/a(n-1) = 10.
PROG
(Python)
def a(n):
lo, hi = 10**(n-1), 10**n
return len(set(a*b for a in range(7, hi//7+1, 10) for b in range(a, hi//a+1, 10) if lo <= a*b < hi))
print([a(n) for n in range(1, 9)]) # Michael S. Branicky, Sep 26 2021
CROSSREFS
KEYWORD
nonn,base,hard,more
AUTHOR
Stefano Spezia, Sep 26 2021
EXTENSIONS
a(9)-a(11) from Michael S. Branicky, Sep 26 2021
a(12)-a(15) from Martin Ehrenstein, Oct 25 2021
STATUS
approved