21137997 has 4 divisors (see below), whose sum is σ = 28184000. Its totient is φ = 14091996.

The previous prime is 21137981. The next prime is 21137999. The reversal of 21137997 is 79973112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21137997 - 2⁴ = 21137981 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21137999) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3522997 + ... + 3523002.

It is an arithmetic number, because the mean of its divisors is an integer number (7046000).

Almost surely, 2^21137997 is an apocalyptic number.

It is an amenable number.

21137997 is a deficient number, since it is larger than the sum of its proper divisors (7046003).

21137997 is an equidigital number, since it uses as much as digits as its factorization.

21137997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7046002.

The product of its digits is 23814, while the sum is 39.

The square root of 21137997 is about 4597.6077475139. The cubic root of 21137997 is about 276.4954213583.

The spelling of 21137997 in words is "twenty-one million, one hundred thirty-seven thousand, nine hundred ninety-seven".