21537613 has 2 divisors, whose sum is σ = 21537614. Its totient is φ = 21537612.

The previous prime is 21537601. The next prime is 21537629. The reversal of 21537613 is 31673512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21511044 + 26569 = 4638^2 + 163^2 .

It is a cyclic number.

It is not a de Polignac number, because 21537613 - 2²¹ = 19440461 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21537643) 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, 10768806 + 10768807.

It is an arithmetic number, because the mean of its divisors is an integer number (10768807).

Almost surely, 2^21537613 is an apocalyptic number.

It is an amenable number.

21537613 is a deficient number, since it is larger than the sum of its proper divisors (1).

21537613 is an equidigital number, since it uses as much as digits as its factorization.

21537613 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3780, while the sum is 28.

The square root of 21537613 is about 4640.8633894998. The cubic root of 21537613 is about 278.2269466441.

The spelling of 21537613 in words is "twenty-one million, five hundred thirty-seven thousand, six hundred thirteen".