21357631 has 4 divisors (see below), whose sum is σ = 21459064. Its totient is φ = 21256200.

The previous prime is 21357619. The next prime is 21357697. The reversal of 21357631 is 13675312.

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

It is a cyclic number.

It is not a de Polignac number, because 21357631 - 2¹⁹ = 20833343 is a prime.

It is a super-2 number, since 2×21357631² = 912296803864322, 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 21357631.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21357031) 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, 50400 + ... + 50821.

It is an arithmetic number, because the mean of its divisors is an integer number (5364766).

Almost surely, 2^21357631 is an apocalyptic number.

21357631 is a deficient number, since it is larger than the sum of its proper divisors (101433).

21357631 is a wasteful number, since it uses less digits than its factorization.

21357631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 101432.

The product of its digits is 3780, while the sum is 28.

The square root of 21357631 is about 4621.4317045695. The cubic root of 21357631 is about 277.4497639225.

The spelling of 21357631 in words is "twenty-one million, three hundred fifty-seven thousand, six hundred thirty-one".