21573637 has 2 divisors, whose sum is σ = 21573638. Its totient is φ = 21573636.

The previous prime is 21573583. The next prime is 21573647. The reversal of 21573637 is 73637512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12609601 + 8964036 = 3551^2 + 2994^2 .

It is a cyclic number.

It is not a de Polignac number, because 21573637 - 2⁷ = 21573509 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21573647) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10786818 + 10786819.

It is an arithmetic number, because the mean of its divisors is an integer number (10786819).

Almost surely, 2^21573637 is an apocalyptic number.

It is an amenable number.

21573637 is a deficient number, since it is larger than the sum of its proper divisors (1).

21573637 is an equidigital number, since it uses as much as digits as its factorization.

21573637 is an evil number, because the sum of its binary digits is even.

The product of its digits is 26460, while the sum is 34.

The square root of 21573637 is about 4644.7429422951. The cubic root of 21573637 is about 278.3819818471.

The spelling of 21573637 in words is "twenty-one million, five hundred seventy-three thousand, six hundred thirty-seven".