21638437 has 4 divisors (see below), whose sum is σ = 22384620. Its totient is φ = 20892256.

The previous prime is 21638431. The next prime is 21638479. The reversal of 21638437 is 73483612.

It is a happy number.

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 5885476 + 15752961 = 2426^2 + 3969^2 .

It is a cyclic number.

It is not a de Polignac number, because 21638437 - 2¹¹ = 21636389 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21638431) 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 in 3 ways as a sum of consecutive naturals, for example, 373048 + ... + 373105.

It is an arithmetic number, because the mean of its divisors is an integer number (5596155).

Almost surely, 2^21638437 is an apocalyptic number.

It is an amenable number.

21638437 is a deficient number, since it is larger than the sum of its proper divisors (746183).

21638437 is an equidigital number, since it uses as much as digits as its factorization.

21638437 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 746182.

The product of its digits is 24192, while the sum is 34.

The square root of 21638437 is about 4651.7133402651. The cubic root of 21638437 is about 278.6604254139.

The spelling of 21638437 in words is "twenty-one million, six hundred thirty-eight thousand, four hundred thirty-seven".