215621 has 4 divisors (see below), whose sum is σ = 246432. Its totient is φ = 184812.

The previous prime is 215617. The next prime is 215653. The reversal of 215621 is 126512.

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 215621 - 2² = 215617 is a prime.

It is a Duffinian number.

It is a plaindrome in base 11.

It is a self number, because there is not a number n which added to its sum of digits gives 215621.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (215681) 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, 15395 + ... + 15408.

It is an arithmetic number, because the mean of its divisors is an integer number (61608).

2²¹⁵⁶²¹ is an apocalyptic number.

It is an amenable number.

215621 is a deficient number, since it is larger than the sum of its proper divisors (30811).

215621 is an equidigital number, since it uses as much as digits as its factorization.

215621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30810.

The product of its digits is 120, while the sum is 17.

The square root of 215621 is about 464.3500834500. The cubic root of 215621 is about 59.9648868625.

The spelling of 215621 in words is "two hundred fifteen thousand, six hundred twenty-one".