21981597 has 8 divisors (see below), whose sum is σ = 31973280. Its totient is φ = 13322160.

The previous prime is 21981593. The next prime is 21981601. The reversal of 21981597 is 79518912.

It is an interprime number because it is at equal distance from previous prime (21981593) and next prime (21981601).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21981597 - 2² = 21981593 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21981593) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 333022 + ... + 333087.

It is an arithmetic number, because the mean of its divisors is an integer number (3996660).

Almost surely, 2^21981597 is an apocalyptic number.

It is an amenable number.

21981597 is a deficient number, since it is larger than the sum of its proper divisors (9991683).

21981597 is a wasteful number, since it uses less digits than its factorization.

21981597 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 666123.

The product of its digits is 45360, while the sum is 42.

The square root of 21981597 is about 4688.4535830058. The cubic root of 21981597 is about 280.1257810734.

It can be divided in two parts, 219815 and 97, that added together give a palindrome (219912).

The spelling of 21981597 in words is "twenty-one million, nine hundred eighty-one thousand, five hundred ninety-seven".