21861291 has 4 divisors (see below), whose sum is σ = 29148392. Its totient is φ = 14574192.

The previous prime is 21861283. The next prime is 21861311. The reversal of 21861291 is 19216812.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21861291 - 2³ = 21861283 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21861221) 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, 3643546 + ... + 3643551.

It is an arithmetic number, because the mean of its divisors is an integer number (7287098).

Almost surely, 2^21861291 is an apocalyptic number.

21861291 is a deficient number, since it is larger than the sum of its proper divisors (7287101).

21861291 is an equidigital number, since it uses as much as digits as its factorization.

21861291 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7287100.

The product of its digits is 1728, while the sum is 30.

The square root of 21861291 is about 4675.6059500347. The cubic root of 21861291 is about 279.6138000479.

The spelling of 21861291 in words is "twenty-one million, eight hundred sixty-one thousand, two hundred ninety-one".