81861431 has 4 divisors (see below), whose sum is σ = 81937152. Its totient is φ = 81785712.

The previous prime is 81861419. The next prime is 81861433. The reversal of 81861431 is 13416818.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 13416818 = 2 ⋅6708409.

It is a cyclic number.

It is not a de Polignac number, because 81861431 - 2²⁶ = 14752567 is a prime.

It is a super-2 number, since 2×81861431² = 13402587770735522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81861433) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 36215 + ... + 38408.

It is an arithmetic number, because the mean of its divisors is an integer number (20484288).

Almost surely, 2^81861431 is an apocalyptic number.

81861431 is a deficient number, since it is larger than the sum of its proper divisors (75721).

81861431 is a wasteful number, since it uses less digits than its factorization.

81861431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 75720.

The product of its digits is 4608, while the sum is 32.

The square root of 81861431 is about 9047.7307099626. The cubic root of 81861431 is about 434.2032909023.

The spelling of 81861431 in words is "eighty-one million, eight hundred sixty-one thousand, four hundred thirty-one".