21731381 has 4 divisors (see below), whose sum is σ = 24835872. Its totient is φ = 18626892.

The previous prime is 21731377. The next prime is 21731417. The reversal of 21731381 is 18313712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21731381 - 2² = 21731377 is a prime.

It is a super-2 number, since 2×21731381² = 944505840334322, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21731381.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21731371) 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, 1552235 + ... + 1552248.

It is an arithmetic number, because the mean of its divisors is an integer number (6208968).

Almost surely, 2^21731381 is an apocalyptic number.

It is an amenable number.

21731381 is a deficient number, since it is larger than the sum of its proper divisors (3104491).

21731381 is an equidigital number, since it uses as much as digits as its factorization.

21731381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3104490.

The product of its digits is 1008, while the sum is 26.

The square root of 21731381 is about 4661.6929328303. The cubic root of 21731381 is about 279.0588340445.

The spelling of 21731381 in words is "twenty-one million, seven hundred thirty-one thousand, three hundred eighty-one".