21613237 has 2 divisors, whose sum is σ = 21613238. Its totient is φ = 21613236.

The previous prime is 21613213. The next prime is 21613243. The reversal of 21613237 is 73231612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21613201 + 36 = 4649^2 + 6^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21613237 is a prime.

It is a plaindrome in base 11.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21613247) 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, 10806618 + 10806619.

It is an arithmetic number, because the mean of its divisors is an integer number (10806619).

Almost surely, 2^21613237 is an apocalyptic number.

It is an amenable number.

21613237 is a deficient number, since it is larger than the sum of its proper divisors (1).

21613237 is an equidigital number, since it uses as much as digits as its factorization.

21613237 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1512, while the sum is 25.

The square root of 21613237 is about 4649.0038717988. The cubic root of 21613237 is about 278.5522079472.

Adding to 21613237 its reverse (73231612), we get a palindrome (94844849).

The spelling of 21613237 in words is "twenty-one million, six hundred thirteen thousand, two hundred thirty-seven".