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A347255
Number of positive integers with n digits that are the product of two integers ending with 4.
5
0, 3, 25, 281, 2941, 30596, 315385, 3231664, 32972224, 335346193, 3402373313, 34454358909, 348373701706, 3518101287286, 35491654274101
OFFSET
1,2
COMMENTS
a(n) is the number of n-digit numbers in A347253.
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(4, hi//4+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, Aug 24 2021
CROSSREFS
Cf. A346509 (ending with 1), A346952 (ending with 3), A337855 (ending with 5), A337856 (ending with 6).
Sequence in context: A118989 A229162 A363354 * A292111 A123989 A001907
KEYWORD
nonn,base,hard,more
AUTHOR
Stefano Spezia, Aug 24 2021
EXTENSIONS
a(9)-a(11) from Michael S. Branicky, Aug 25 2021
a(12)-a(15) from Martin Ehrenstein, Sep 29 2021
STATUS
approved