21981257 has 4 divisors (see below), whose sum is σ = 22013316. Its totient is φ = 21949200.

The previous prime is 21981251. The next prime is 21981283. The reversal of 21981257 is 75218912.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 17774656 + 4206601 = 4216^2 + 2051^2 .

It is a cyclic number.

It is not a de Polignac number, because 21981257 - 2²⁴ = 5204041 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21981251) 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, 14978 + ... + 16379.

It is an arithmetic number, because the mean of its divisors is an integer number (5503329).

Almost surely, 2^21981257 is an apocalyptic number.

It is an amenable number.

21981257 is a deficient number, since it is larger than the sum of its proper divisors (32059).

21981257 is an equidigital number, since it uses as much as digits as its factorization.

21981257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32058.

The product of its digits is 10080, while the sum is 35.

The square root of 21981257 is about 4688.4173235752. The cubic root of 21981257 is about 280.1243367856.

The spelling of 21981257 in words is "twenty-one million, nine hundred eighty-one thousand, two hundred fifty-seven".