21375981 has 36 divisors (see below), whose sum is σ = 35243936. Its totient is φ = 12937320.

The previous prime is 21375971. The next prime is 21376009. The reversal of 21375981 is 18957312.

It is not a de Polignac number, because 21375981 - 2⁶ = 21375917 is a prime.

It is a super-2 number, since 2×21375981² = 913865127424722, 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 (21375961) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 29040 + ... + 29766.

Almost surely, 2^21375981 is an apocalyptic number.

It is an amenable number.

21375981 is a deficient number, since it is larger than the sum of its proper divisors (13867955).

21375981 is an equidigital number, since it uses as much as digits as its factorization.

21375981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 764 (or 741 counting only the distinct ones).

The product of its digits is 15120, while the sum is 36.

The square root of 21375981 is about 4623.4165938189. The cubic root of 21375981 is about 277.5292007256.

It can be divided in two parts, 2137 and 5981, that added together give a palindrome (8118).

The spelling of 21375981 in words is "twenty-one million, three hundred seventy-five thousand, nine hundred eighty-one".