21981457 has 4 divisors (see below), whose sum is σ = 22093236. Its totient is φ = 21869680.

The previous prime is 21981451. The next prime is 21981469. The reversal of 21981457 is 75418912.

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 21818241 + 163216 = 4671^2 + 404^2 .

It is a cyclic number.

It is not a de Polignac number, because 21981457 - 2⁷ = 21981329 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21981451) 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, 55594 + ... + 55987.

It is an arithmetic number, because the mean of its divisors is an integer number (5523309).

Almost surely, 2^21981457 is an apocalyptic number.

It is an amenable number.

21981457 is a deficient number, since it is larger than the sum of its proper divisors (111779).

21981457 is a wasteful number, since it uses less digits than its factorization.

21981457 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 111778.

The product of its digits is 20160, while the sum is 37.

The square root of 21981457 is about 4688.4386526860. The cubic root of 21981457 is about 280.1251863685.

It can be divided in two parts, 2198 and 1457, that added together give a triangular number (3655 = T₈₅).

The spelling of 21981457 in words is "twenty-one million, nine hundred eighty-one thousand, four hundred fifty-seven".