20216661 has 4 divisors (see below), whose sum is σ = 26955552. Its totient is φ = 13477772.

The previous prime is 20216659. The next prime is 20216699. The reversal of 20216661 is 16661202.

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 20216661 - 2¹ = 20216659 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20216641) 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, 3369441 + ... + 3369446.

It is an arithmetic number, because the mean of its divisors is an integer number (6738888).

Almost surely, 2^20216661 is an apocalyptic number.

It is an amenable number.

20216661 is a deficient number, since it is larger than the sum of its proper divisors (6738891).

20216661 is an equidigital number, since it uses as much as digits as its factorization.

20216661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6738890.

The product of its (nonzero) digits is 864, while the sum is 24.

The square root of 20216661 is about 4496.2941407341. The cubic root of 20216661 is about 272.4184240850.

Adding to 20216661 its reverse (16661202), we get a palindrome (36877863).

The spelling of 20216661 in words is "twenty million, two hundred sixteen thousand, six hundred sixty-one".