21421657 has 2 divisors, whose sum is σ = 21421658. Its totient is φ = 21421656.

The previous prime is 21421627. The next prime is 21421667. The reversal of 21421657 is 75612412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16475481 + 4946176 = 4059^2 + 2224^2 .

It is a cyclic number.

It is not a de Polignac number, because 21421657 - 2²³ = 13033049 is a prime.

It is not a weakly prime, because it can be changed into another prime (21421627) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10710828 + 10710829.

It is an arithmetic number, because the mean of its divisors is an integer number (10710829).

Almost surely, 2^21421657 is an apocalyptic number.

It is an amenable number.

21421657 is a deficient number, since it is larger than the sum of its proper divisors (1).

21421657 is an equidigital number, since it uses as much as digits as its factorization.

21421657 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3360, while the sum is 28.

The square root of 21421657 is about 4628.3535949623. The cubic root of 21421657 is about 277.7267340461.

The spelling of 21421657 in words is "twenty-one million, four hundred twenty-one thousand, six hundred fifty-seven".