A308983 -id:A308983 - cp's OEIS frontend

A327435 a(n) is the largest (2n+1)-digit palindrome that is the product of two numbers having an equal number of digits.

9, 999, 99999, 9999999, 999969999, 99999999999, 9999998999999, 999999999999999, 99999999799999999, 9999999997999999999, 999999999999999999999, 99999999999899999999999, 9999999999999999999999999, 999999999999979999999999999, 99999999999999999999999999999, 9999999999999996999999999999999

Offset: 0

Chai Wah Wu, Oct 03 2019

A308803 is the union of this sequence and A327897. This sequence lists the terms of odd indices of A308803 as they seem to be easier to compute than terms of even indices of A308803 (the sequence A327897).

			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

Chai Wah Wu, Table of n, a(n) for n = 0..89

Cf. A002113, A308803, A308983, A327897.

a(n) = A308803(2n+1).

a(n) >= (2*10^n-1)(5*10^n+1) = 10^(2n+1)-3*10^n-1. If n is a term of A308983, then a(n) = 10^(2n+1)-3*10^n-1.

cp's OEIS Frontend

A327435 a(n) is the largest (2n+1)-digit palindrome that is the product of two numbers having an equal number of digits.

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