21315137 has 2 divisors, whose sum is σ = 21315138. Its totient is φ = 21315136.

The previous prime is 21315109. The next prime is 21315139. The reversal of 21315137 is 73151312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18931201 + 2383936 = 4351^2 + 1544^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21315137 is a prime.

Together with 21315139, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21315139) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10657568 + 10657569.

It is an arithmetic number, because the mean of its divisors is an integer number (10657569).

Almost surely, 2^21315137 is an apocalyptic number.

It is an amenable number.

21315137 is a deficient number, since it is larger than the sum of its proper divisors (1).

21315137 is an equidigital number, since it uses as much as digits as its factorization.

21315137 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 630, while the sum is 23.

The square root of 21315137 is about 4616.8319224334. The cubic root of 21315137 is about 277.2656333546.

Adding to 21315137 its reverse (73151312), we get a palindrome (94466449).

The spelling of 21315137 in words is "twenty-one million, three hundred fifteen thousand, one hundred thirty-seven".