21391191 has 12 divisors (see below), whose sum is σ = 30944160. Its totient is φ = 14239680.

The previous prime is 21391189. The next prime is 21391193. The reversal of 21391191 is 19119312.

It is an interprime number because it is at equal distance from previous prime (21391189) and next prime (21391193).

It is not a de Polignac number, because 21391191 - 2¹ = 21391189 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21391193) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6895 + ... + 9503.

It is an arithmetic number, because the mean of its divisors is an integer number (2578680).

Almost surely, 2^21391191 is an apocalyptic number.

21391191 is a deficient number, since it is larger than the sum of its proper divisors (9552969).

21391191 is a wasteful number, since it uses less digits than its factorization.

21391191 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3526 (or 3523 counting only the distinct ones).

The product of its digits is 486, while the sum is 27.

The square root of 21391191 is about 4625.0611887844. The cubic root of 21391191 is about 277.5950100770.

The spelling of 21391191 in words is "twenty-one million, three hundred ninety-one thousand, one hundred ninety-one".