21372157 has 2 divisors, whose sum is σ = 21372158. Its totient is φ = 21372156.

The previous prime is 21372151. The next prime is 21372167. The reversal of 21372157 is 75127312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16818201 + 4553956 = 4101^2 + 2134^2 .

It is a cyclic number.

It is not a de Polignac number, because 21372157 - 2³ = 21372149 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21372151) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10686078 + 10686079.

It is an arithmetic number, because the mean of its divisors is an integer number (10686079).

Almost surely, 2^21372157 is an apocalyptic number.

It is an amenable number.

21372157 is a deficient number, since it is larger than the sum of its proper divisors (1).

21372157 is an equidigital number, since it uses as much as digits as its factorization.

21372157 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2940, while the sum is 28.

The square root of 21372157 is about 4623.0030283356. The cubic root of 21372157 is about 277.5126504527.

Subtracting from 21372157 its sum of digits (28), we obtain a square (21372129 = 4623²).

Adding to 21372157 its reverse (75127312), we get a palindrome (96499469).

The spelling of 21372157 in words is "twenty-one million, three hundred seventy-two thousand, one hundred fifty-seven".