21361891 has 8 divisors (see below), whose sum is σ = 21723104. Its totient is φ = 21003840.

The previous prime is 21361889. The next prime is 21361897. The reversal of 21361891 is 19816312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21361891 - 2¹ = 21361889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21361897) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15511 + ... + 16831.

It is an arithmetic number, because the mean of its divisors is an integer number (2715388).

Almost surely, 2^21361891 is an apocalyptic number.

21361891 is a deficient number, since it is larger than the sum of its proper divisors (361213).

21361891 is a wasteful number, since it uses less digits than its factorization.

21361891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1581.

The product of its digits is 2592, while the sum is 31.

The square root of 21361891 is about 4621.8925777218. The cubic root of 21361891 is about 277.4682094361.

The spelling of 21361891 in words is "twenty-one million, three hundred sixty-one thousand, eight hundred ninety-one".