21520637 has 2 divisors, whose sum is σ = 21520638. Its totient is φ = 21520636.

The previous prime is 21520607. The next prime is 21520649. The reversal of 21520637 is 73602512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13980121 + 7540516 = 3739^2 + 2746^2 .

It is a cyclic number.

It is not a de Polignac number, because 21520637 - 2⁶ = 21520573 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21520607) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760318 + 10760319.

It is an arithmetic number, because the mean of its divisors is an integer number (10760319).

Almost surely, 2^21520637 is an apocalyptic number.

It is an amenable number.

21520637 is a deficient number, since it is larger than the sum of its proper divisors (1).

21520637 is an equidigital number, since it uses as much as digits as its factorization.

21520637 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2520, while the sum is 26.

The square root of 21520637 is about 4639.0340589394. The cubic root of 21520637 is about 278.1538277067.

The spelling of 21520637 in words is "twenty-one million, five hundred twenty thousand, six hundred thirty-seven".