21657901 has 2 divisors, whose sum is σ = 21657902. Its totient is φ = 21657900.

The previous prime is 21657877. The next prime is 21657943. The reversal of 21657901 is 10975612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11088900 + 10569001 = 3330^2 + 3251^2 .

It is a cyclic number.

It is not a de Polignac number, because 21657901 - 2⁷ = 21657773 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21657971) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10828950 + 10828951.

It is an arithmetic number, because the mean of its divisors is an integer number (10828951).

Almost surely, 2^21657901 is an apocalyptic number.

It is an amenable number.

21657901 is a deficient number, since it is larger than the sum of its proper divisors (1).

21657901 is an equidigital number, since it uses as much as digits as its factorization.

21657901 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3780, while the sum is 31.

The square root of 21657901 is about 4653.8050023610. The cubic root of 21657901 is about 278.7439530283.

The spelling of 21657901 in words is "twenty-one million, six hundred fifty-seven thousand, nine hundred one".