21309381 has 48 divisors (see below), whose sum is σ = 34594560. Its totient is φ = 12579840.

The previous prime is 21309341. The next prime is 21309383. The reversal of 21309381 is 18390312.

It is not a de Polignac number, because 21309381 - 2¹¹ = 21307333 is a prime.

It is a super-2 number, since 2×21309381² = 908179437206322, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21309383) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 269700 + ... + 269778.

It is an arithmetic number, because the mean of its divisors is an integer number (720720).

Almost surely, 2^21309381 is an apocalyptic number.

It is an amenable number.

21309381 is a deficient number, since it is larger than the sum of its proper divisors (13285179).

21309381 is a wasteful number, since it uses less digits than its factorization.

21309381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 186 (or 183 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21309381 is about 4616.2085091555. The cubic root of 21309381 is about 277.2406732419.

Adding to 21309381 its reverse (18390312), we get a palindrome (39699693).

It can be divided in two parts, 2130 and 9381, that added together give a palindrome (11511).

The spelling of 21309381 in words is "twenty-one million, three hundred nine thousand, three hundred eighty-one".