21306157 has 4 divisors (see below), whose sum is σ = 21315580. Its totient is φ = 21296736.

The previous prime is 21306149. The next prime is 21306167. The reversal of 21306157 is 75160312.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 17189316 + 4116841 = 4146^2 + 2029^2 .

It is a 3-Lehmer number, since φ(21306157) divides (21306157-1)³.

It is a cyclic number.

It is not a de Polignac number, because 21306157 - 2³ = 21306149 is a prime.

It is a super-2 number, since 2×21306157² = 907904652217298, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21306167) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 943 + ... + 6595.

It is an arithmetic number, because the mean of its divisors is an integer number (5328895).

It is a Poulet number, since it divides 2^21306156-1.

Almost surely, 2^21306157 is an apocalyptic number.

21306157 is the 3769-th pentagonal number.

It is an amenable number.

21306157 is a deficient number, since it is larger than the sum of its proper divisors (9423).

21306157 is an equidigital number, since it uses as much as digits as its factorization.

21306157 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9422.

The product of its (nonzero) digits is 1260, while the sum is 25.

The square root of 21306157 is about 4615.8592916162. The cubic root of 21306157 is about 277.2266908397.

Adding to 21306157 its reverse (75160312), we get a palindrome (96466469).

The spelling of 21306157 in words is "twenty-one million, three hundred six thousand, one hundred fifty-seven".