A347255 Number of positive integers with n digits that are the product of two integers ending with 4.

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.

Links

Table of n, a(n) for n=1..15.

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. A017341, A052268, A347253.

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

Adjacent sequences: A347252 A347253 A347254 * A347256 A347257 A347258

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