21861901 has 4 divisors (see below), whose sum is σ = 21891100. Its totient is φ = 21832704.

The previous prime is 21861893. The next prime is 21861971. The reversal of 21861901 is 10916812.

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 7986276 + 13875625 = 2826^2 + 3725^2 .

It is a cyclic number.

It is not a de Polignac number, because 21861901 - 2³ = 21861893 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 21861901.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21861971) 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, 13446 + ... + 14983.

It is an arithmetic number, because the mean of its divisors is an integer number (5472775).

Almost surely, 2^21861901 is an apocalyptic number.

21861901 is the 2700-th hex number.

It is an amenable number.

21861901 is a deficient number, since it is larger than the sum of its proper divisors (29199).

21861901 is an equidigital number, since it uses as much as digits as its factorization.

21861901 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29198.

The product of its (nonzero) digits is 864, while the sum is 28.

The square root of 21861901 is about 4675.6711817663. The cubic root of 21861901 is about 279.6164007304.

The spelling of 21861901 in words is "twenty-one million, eight hundred sixty-one thousand, nine hundred one".