OFFSET
1,2
COMMENTS
a(n) is the number of n-digit numbers in A324297.
FORMULA
Conjecture: Lim_{n->infinity} a(n)/a(n-1) = 10.
PROG
(Python)
def A337856(n):
k, n1, n2, pset = 0, 10**(n-1)//2-18, 10**n//2-18, set()
while 50*k**2+60*k < n2:
a, b = divmod(n1-30*k, 50*k+30)
m = max(k, a+int(b>0))
r = 50*k*m+30*(k+m)
while r < n2:
pset.add(r)
m += 1
r += 50*k+30
k += 1
return len(pset) # Chai Wah Wu, Sep 26 2021
CROSSREFS
KEYWORD
nonn,base,hard,more
AUTHOR
Stefano Spezia, Sep 27 2020
EXTENSIONS
a(5) corrected by and a(6)-a(9) from Jinyuan Wang, Oct 01 2020
a(10)-a(13) from Bert Dobbelaere, Oct 20 2020
a(14) from Martin Ehrenstein, Aug 06 2021
STATUS
approved