21609381 has 8 divisors (see below), whose sum is σ = 28833984. Its totient is φ = 14395520.

The previous prime is 21609377. The next prime is 21609389. The reversal of 21609381 is 18390612.

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 21609381 - 2² = 21609377 is a prime.

It is a super-2 number, since 2×21609381² = 933930694406322, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21609389) 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, 6616 + ... + 9326.

It is an arithmetic number, because the mean of its divisors is an integer number (3604248).

Almost surely, 2^21609381 is an apocalyptic number.

It is an amenable number.

21609381 is a deficient number, since it is larger than the sum of its proper divisors (7224603).

21609381 is a wasteful number, since it uses less digits than its factorization.

21609381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5371.

The product of its (nonzero) digits is 2592, while the sum is 30.

The square root of 21609381 is about 4648.5891408039. The cubic root of 21609381 is about 278.5356415378.

Adding to 21609381 its reverse (18390612), we get a palindrome (39999993).

The spelling of 21609381 in words is "twenty-one million, six hundred nine thousand, three hundred eighty-one".