21356957 has 4 divisors (see below), whose sum is σ = 21440316. Its totient is φ = 21273600.

The previous prime is 21356927. The next prime is 21356971. The reversal of 21356957 is 75965312.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 17799961 + 3556996 = 4219^2 + 1886^2 .

It is a cyclic number.

It is not a de Polignac number, because 21356957 - 2¹² = 21352861 is a prime.

It is a super-2 number, since 2×21356957² = 912239224599698, 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 21356957.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21356917) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 41294 + ... + 41807.

It is an arithmetic number, because the mean of its divisors is an integer number (5360079).

Almost surely, 2^21356957 is an apocalyptic number.

It is an amenable number.

21356957 is a deficient number, since it is larger than the sum of its proper divisors (83359).

21356957 is an equidigital number, since it uses as much as digits as its factorization.

21356957 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 83358.

The product of its digits is 56700, while the sum is 38.

The square root of 21356957 is about 4621.3587828690. The cubic root of 21356957 is about 277.4468453231.

The spelling of 21356957 in words is "twenty-one million, three hundred fifty-six thousand, nine hundred fifty-seven".