21157901 has 2 divisors, whose sum is σ = 21157902. Its totient is φ = 21157900.

The previous prime is 21157897. The next prime is 21157919. The reversal of 21157901 is 10975112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20475625 + 682276 = 4525^2 + 826^2 .

It is a cyclic number.

It is not a de Polignac number, because 21157901 - 2² = 21157897 is a prime.

It is equal to p_1339307 and since 21157901 and 1339307 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21157921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10578950 + 10578951.

It is an arithmetic number, because the mean of its divisors is an integer number (10578951).

Almost surely, 2^21157901 is an apocalyptic number.

It is an amenable number.

21157901 is a deficient number, since it is larger than the sum of its proper divisors (1).

21157901 is an equidigital number, since it uses as much as digits as its factorization.

21157901 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 630, while the sum is 26.

The square root of 21157901 is about 4599.7718421678. The cubic root of 21157901 is about 276.5821788438.

The spelling of 21157901 in words is "twenty-one million, one hundred fifty-seven thousand, nine hundred one".