21315591 has 12 divisors (see below), whose sum is σ = 33588360. Its totient is φ = 12918480.

The previous prime is 21315583. The next prime is 21315599. The reversal of 21315591 is 19551312.

It is an interprime number because it is at equal distance from previous prime (21315583) and next prime (21315599).

It is not a de Polignac number, because 21315591 - 2³ = 21315583 is a prime.

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21315599) 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, 107556 + ... + 107753.

It is an arithmetic number, because the mean of its divisors is an integer number (2799030).

Almost surely, 2^21315591 is an apocalyptic number.

21315591 is a deficient number, since it is larger than the sum of its proper divisors (12272769).

21315591 is a wasteful number, since it uses less digits than its factorization.

21315591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 215326 (or 215323 counting only the distinct ones).

The product of its digits is 1350, while the sum is 27.

The square root of 21315591 is about 4616.8810900867. The cubic root of 21315591 is about 277.2676018728.

The spelling of 21315591 in words is "twenty-one million, three hundred fifteen thousand, five hundred ninety-one".