21287397 has 16 divisors (see below), whose sum is σ = 30181248. Its totient is φ = 13316160.

The previous prime is 21287393. The next prime is 21287407. The reversal of 21287397 is 79378212.

It is not a de Polignac number, because 21287397 - 2² = 21287393 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21287393) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 747 + ... + 6567.

It is an arithmetic number, because the mean of its divisors is an integer number (1886328).

Almost surely, 2^21287397 is an apocalyptic number.

It is an amenable number.

21287397 is a deficient number, since it is larger than the sum of its proper divisors (8893851).

21287397 is a wasteful number, since it uses less digits than its factorization.

21287397 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5900.

The product of its digits is 42336, while the sum is 39.

The square root of 21287397 is about 4613.8267197631. The cubic root of 21287397 is about 277.1453012224.

The spelling of 21287397 in words is "twenty-one million, two hundred eighty-seven thousand, three hundred ninety-seven".