21563957 has 4 divisors (see below), whose sum is σ = 21653676. Its totient is φ = 21474240.

The previous prime is 21563947. The next prime is 21563959. The reversal of 21563957 is 75936512.

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 5635876 + 15928081 = 2374^2 + 3991^2 .

It is a cyclic number.

It is not a de Polignac number, because 21563957 - 2¹² = 21559861 is a prime.

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 21563957.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21563959) 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, 44498 + ... + 44979.

It is an arithmetic number, because the mean of its divisors is an integer number (5413419).

Almost surely, 2^21563957 is an apocalyptic number.

It is an amenable number.

21563957 is a deficient number, since it is larger than the sum of its proper divisors (89719).

21563957 is an equidigital number, since it uses as much as digits as its factorization.

21563957 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 89718.

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

The square root of 21563957 is about 4643.7007870878. The cubic root of 21563957 is about 278.3403393442.

It can be divided in two parts, 2156395 and 7, that multiplied together give a triangular number (15094765 = T₅₄₉₄).

The spelling of 21563957 in words is "twenty-one million, five hundred sixty-three thousand, nine hundred fifty-seven".