21365657 has 2 divisors, whose sum is σ = 21365658. Its totient is φ = 21365656.

The previous prime is 21365647. The next prime is 21365699. The reversal of 21365657 is 75656312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13808656 + 7557001 = 3716^2 + 2749^2 .

It is a cyclic number.

It is not a de Polignac number, because 21365657 - 2⁶ = 21365593 is a prime.

It is not a weakly prime, because it can be changed into another prime (21365647) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10682828 + 10682829.

It is an arithmetic number, because the mean of its divisors is an integer number (10682829).

Almost surely, 2^21365657 is an apocalyptic number.

It is an amenable number.

21365657 is a deficient number, since it is larger than the sum of its proper divisors (1).

21365657 is an equidigital number, since it uses as much as digits as its factorization.

21365657 is an evil number, because the sum of its binary digits is even.

The product of its digits is 37800, while the sum is 35.

The square root of 21365657 is about 4622.2999686303. The cubic root of 21365657 is about 277.4845139209.

It can be divided in two parts, 21365 and 657, that added together give a palindrome (22022).

The spelling of 21365657 in words is "twenty-one million, three hundred sixty-five thousand, six hundred fifty-seven".