21856901 has 4 divisors (see below), whose sum is σ = 23843904. Its totient is φ = 19869900.

The previous prime is 21856889. The next prime is 21856903. The reversal of 21856901 is 10965812.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21856901 - 2⁶ = 21856837 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21856903) 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, 993485 + ... + 993506.

It is an arithmetic number, because the mean of its divisors is an integer number (5960976).

Almost surely, 2^21856901 is an apocalyptic number.

It is an amenable number.

21856901 is a deficient number, since it is larger than the sum of its proper divisors (1987003).

21856901 is a wasteful number, since it uses less digits than its factorization.

21856901 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1987002.

The product of its (nonzero) digits is 4320, while the sum is 32.

The square root of 21856901 is about 4675.1364685964. The cubic root of 21856901 is about 279.5950822336.

The spelling of 21856901 in words is "twenty-one million, eight hundred fifty-six thousand, nine hundred one".