This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
a(2) = 99 * 91 = 9009, a(3) = 993 * 913 = 906609.
def is_palindrome(n):
if n<10: return True
n = str(n)
midpoint = int(len(n)/2)
return n[:midpoint] == n[-midpoint:][::-1]
def A327897(n):
lower_bound = 10**(n-1) - 1
upper_bound = 10**n - 1
max_palindromes = (0,0,0)
for n1 in range(upper_bound, lower_bound, -1):
for n2 in range(n1, lower_bound, -1):
n = n1* n2
if is_palindrome(n) and n>max_palindromes[2]:
max_palindromes = (n1, n2, n)
if n < max_palindromes[2]:
break
if n1*n1 < max_palindromes[2]:
break
return max_palindromes
if _name_ == '_main_':
for n in range(1,7):
print(A327897(n))
a(0) = 9 = 3 * 3 a(1) = 999 = 27 * 37 a(2) = 99999 = 123 * 813 a(3) = 9999999 = 2151 * 4649 a(4) = 999969999 = 16667 * 59997 a(5) = 99999999999 = 194841 * 513239 a(6) = 9999998999999 = 2893921 * 3455519 a(7) = 999999999999999 = 11099889 * 90090991 a(8) = 99999999799999999 = 265412903 * 376771433 a(9) = 9999999997999999999 = 2441330309 * 4096127411 a(10) = 999999999999999999999 = 19845575559 * 50389065161 a(11) = 99999999999899999999999 = 345867517613 * 289128047323
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