81969813 has 10 divisors (see below), whose sum is σ = 122448854. Its totient is φ = 54646488.

The previous prime is 81969809. The next prime is 81969841. The reversal of 81969813 is 31896918.

It can be written as a sum of positive squares in only one way, i.e., 71876484 + 10093329 = 8478^2 + 3177^2 .

It is not a de Polignac number, because 81969813 - 2² = 81969809 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81969313) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 505906 + ... + 506067.

Almost surely, 2^81969813 is an apocalyptic number.

It is an amenable number.

81969813 is a deficient number, since it is larger than the sum of its proper divisors (40479041).

81969813 is a wasteful number, since it uses less digits than its factorization.

81969813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1011985 (or 1011976 counting only the distinct ones).

The product of its digits is 93312, while the sum is 45.

The square root of 81969813 is about 9053.7181864690. The cubic root of 81969813 is about 434.3948303008.

The spelling of 81969813 in words is "eighty-one million, nine hundred sixty-nine thousand, eight hundred thirteen".