21397015 has 16 divisors (see below), whose sum is σ = 27422208. Its totient is φ = 15988896.

The previous prime is 21397009. The next prime is 21397043. The reversal of 21397015 is 51079312.

It is a cyclic number.

It is not a de Polignac number, because 21397015 - 2³ = 21397007 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2782 + ... + 7108.

It is an arithmetic number, because the mean of its divisors is an integer number (1713888).

Almost surely, 2^21397015 is an apocalyptic number.

21397015 is a deficient number, since it is larger than the sum of its proper divisors (6025193).

21397015 is a wasteful number, since it uses less digits than its factorization.

21397015 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4398.

The product of its (nonzero) digits is 1890, while the sum is 28.

The square root of 21397015 is about 4625.6907592272. The cubic root of 21397015 is about 277.6202006121.

Multiplying 21397015 by its sum of digits (28), we get a triangular number (599116420 = T₃₄₆₁₅).

The spelling of 21397015 in words is "twenty-one million, three hundred ninety-seven thousand, fifteen".