21487621 has 4 divisors (see below), whose sum is σ = 21746592. Its totient is φ = 21228652.

The previous prime is 21487597. The next prime is 21487667. The reversal of 21487621 is 12678412.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21487621 - 2¹³ = 21479429 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 (21487421) 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, 129361 + ... + 129526.

It is an arithmetic number, because the mean of its divisors is an integer number (5436648).

Almost surely, 2^21487621 is an apocalyptic number.

It is an amenable number.

21487621 is a deficient number, since it is larger than the sum of its proper divisors (258971).

21487621 is an equidigital number, since it uses as much as digits as its factorization.

21487621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 258970.

The product of its digits is 5376, while the sum is 31.

The square root of 21487621 is about 4635.4741936505. The cubic root of 21487621 is about 278.0115111773.

The spelling of 21487621 in words is "twenty-one million, four hundred eighty-seven thousand, six hundred twenty-one".