21647953 has 4 divisors (see below), whose sum is σ = 22921380. Its totient is φ = 20374528.

The previous prime is 21647939. The next prime is 21647957. The reversal of 21647953 is 35974612.

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 13162384 + 8485569 = 3628^2 + 2913^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21647953 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21647957) 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, 636688 + ... + 636721.

It is an arithmetic number, because the mean of its divisors is an integer number (5730345).

Almost surely, 2^21647953 is an apocalyptic number.

It is an amenable number.

21647953 is a deficient number, since it is larger than the sum of its proper divisors (1273427).

21647953 is a wasteful number, since it uses less digits than its factorization.

21647953 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1273426.

The product of its digits is 45360, while the sum is 37.

The square root of 21647953 is about 4652.7360767617. The cubic root of 21647953 is about 278.7012685362.

The spelling of 21647953 in words is "twenty-one million, six hundred forty-seven thousand, nine hundred fifty-three".