21981657 has 4 divisors (see below), whose sum is σ = 29308880. Its totient is φ = 14654436.

The previous prime is 21981653. The next prime is 21981667. The reversal of 21981657 is 75618912.

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 21981657 - 2² = 21981653 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21981653) 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, 3663607 + ... + 3663612.

It is an arithmetic number, because the mean of its divisors is an integer number (7327220).

Almost surely, 2^21981657 is an apocalyptic number.

It is an amenable number.

21981657 is a deficient number, since it is larger than the sum of its proper divisors (7327223).

21981657 is an equidigital number, since it uses as much as digits as its factorization.

21981657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7327222.

The product of its digits is 30240, while the sum is 39.

The square root of 21981657 is about 4688.4599816997. The cubic root of 21981657 is about 280.1260359462.

The spelling of 21981657 in words is "twenty-one million, nine hundred eighty-one thousand, six hundred fifty-seven".