81613881 has 6 divisors (see below), whose sum is σ = 117886730. Its totient is φ = 54409248.

The previous prime is 81613877. The next prime is 81613901. The reversal of 81613881 is 18831618.

It can be written as a sum of positive squares in only one way, i.e., 59907600 + 21706281 = 7740^2 + 4659^2 .

It is not a de Polignac number, because 81613881 - 2² = 81613877 is a prime.

It is a super-2 number, since 2×81613881² = 13321651143764322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81613381) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4534096 + ... + 4534113.

Almost surely, 2^81613881 is an apocalyptic number.

It is an amenable number.

81613881 is a deficient number, since it is larger than the sum of its proper divisors (36272849).

81613881 is a wasteful number, since it uses less digits than its factorization.

81613881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9068215 (or 9068212 counting only the distinct ones).

The product of its digits is 9216, while the sum is 36.

The square root of 81613881 is about 9034.0401261008. The cubic root of 81613881 is about 433.7651702346.

The spelling of 81613881 in words is "eighty-one million, six hundred thirteen thousand, eight hundred eighty-one".