21555901 has 4 divisors (see below), whose sum is σ = 21577500. Its totient is φ = 21534304.

The previous prime is 21555893. The next prime is 21555917. The reversal of 21555901 is 10955512.

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 20484676 + 1071225 = 4526^2 + 1035^2 .

It is a cyclic number.

It is not a de Polignac number, because 21555901 - 2³ = 21555893 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 21555901.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21555931) 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, 9226 + ... + 11323.

It is an arithmetic number, because the mean of its divisors is an integer number (5394375).

Almost surely, 2^21555901 is an apocalyptic number.

It is an amenable number.

21555901 is a deficient number, since it is larger than the sum of its proper divisors (21599).

21555901 is a wasteful number, since it uses less digits than its factorization.

21555901 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21598.

The product of its (nonzero) digits is 2250, while the sum is 28.

The square root of 21555901 is about 4642.8332944442. The cubic root of 21555901 is about 278.3056736431.

The spelling of 21555901 in words is "twenty-one million, five hundred fifty-five thousand, nine hundred one".