### Properties of the number 81813:

81813 = 3 × 27271 is semiprime and squarefree.81813 has 2 distinct prime factors, 4 divisors, 33 antidivisors and 54540 totatives.

81813 has a semiprime digit sum 21 in base 10.

81813 has a Fibonacci digit sum 21 in base 10.

81813 has a triangular digit sum 21 in base 10.

Reversing the decimal digits of 81813 results in a sphenic number.

81813 = 40907

^{2}- 40906

^{2}= 13637

^{2}- 13634

^{2}is the difference of 2 nonnegative squares in 2 ways.

81813 is the sum of 2 positive triangular numbers.

81813 is the difference of 2 positive pentagonal numbers in 1 way.

81813 is the difference of 2 positive pentagonal pyramidal numbers in 1 way.

81813 = 1

^{2}+ 4

^{2}+ 286

^{2}is the sum of 3 positive squares.

81813

^{2}is the sum of 3 positive squares.

81813 is a proper divisor of 1901

^{54}- 1.

81813 is an emirpimes in (at least) the following bases: 3, 6, 7, 9, 15, 19, 33, 35, 48, 51, 55, 61, 67, 71, 78, 81, 85, and 99.

81813 is palindromic in (at least) base -55.

81813 in base 54 = S33 and consists of only the digits '3' and 'S'.

### The number 81813 belongs to the following On-Line Encyclopedia of Integer Sequences (OEIS) sequences (among others):

Sequence numbers and descriptions below are taken from OEIS.A053948: Numbers n such that n^2 contains only digits {3,6,9}.

A137041: Numbers n such that n and the square of n use only the digits 1, 3, 6, 8 and 9.

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