21351637 has 2 divisors, whose sum is σ = 21351638. Its totient is φ = 21351636.

The previous prime is 21351619. The next prime is 21351661. The reversal of 21351637 is 73615312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16573041 + 4778596 = 4071^2 + 2186^2 .

It is a cyclic number.

It is not a de Polignac number, because 21351637 - 2⁷ = 21351509 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21355637) 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, 10675818 + 10675819.

It is an arithmetic number, because the mean of its divisors is an integer number (10675819).

Almost surely, 2^21351637 is an apocalyptic number.

It is an amenable number.

21351637 is a deficient number, since it is larger than the sum of its proper divisors (1).

21351637 is an equidigital number, since it uses as much as digits as its factorization.

21351637 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 21351637 is about 4620.7831587297. The cubic root of 21351637 is about 277.4238061515.

Adding to 21351637 its reverse (73615312), we get a palindrome (94966949).

The spelling of 21351637 in words is "twenty-one million, three hundred fifty-one thousand, six hundred thirty-seven".