21137605 has 4 divisors (see below), whose sum is σ = 25365132. Its totient is φ = 16910080.

The previous prime is 21137563. The next prime is 21137609. The reversal of 21137605 is 50673112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11792356 + 9345249 = 3434^2 + 3057^2 .

It is not a de Polignac number, because 21137605 - 2²¹ = 19040453 is a prime.

It is a Duffinian number.

It is a plaindrome in base 7.

It is a self number, because there is not a number n which added to its sum of digits gives 21137605.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21137609) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2113756 + ... + 2113765.

It is an arithmetic number, because the mean of its divisors is an integer number (6341283).

Almost surely, 2^21137605 is an apocalyptic number.

It is an amenable number.

21137605 is a deficient number, since it is larger than the sum of its proper divisors (4227527).

21137605 is an equidigital number, since it uses as much as digits as its factorization.

21137605 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4227526.

The product of its (nonzero) digits is 1260, while the sum is 25.

The square root of 21137605 is about 4597.5651164502. The cubic root of 21137605 is about 276.4937121633.

The spelling of 21137605 in words is "twenty-one million, one hundred thirty-seven thousand, six hundred five".