81649381 has 8 divisors (see below), whose sum is σ = 91945728. Its totient is φ = 71832000.

The previous prime is 81649369. The next prime is 81649411. The reversal of 81649381 is 18394618.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81649381 - 2⁹ = 81648869 is a prime.

It is a super-2 number, since 2×81649381² = 13333242835366322, 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 (81641381) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 119380 + ... + 120061.

It is an arithmetic number, because the mean of its divisors is an integer number (11493216).

Almost surely, 2^81649381 is an apocalyptic number.

It is an amenable number.

81649381 is a deficient number, since it is larger than the sum of its proper divisors (10296347).

81649381 is a wasteful number, since it uses less digits than its factorization.

81649381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 239483.

The product of its digits is 41472, while the sum is 40.

The square root of 81649381 is about 9036.0047034074. The cubic root of 81649381 is about 433.8280534567.

The spelling of 81649381 in words is "eighty-one million, six hundred forty-nine thousand, three hundred eighty-one".