20756561 has 4 divisors (see below), whose sum is σ = 23721792. Its totient is φ = 17791332.

The previous prime is 20756521. The next prime is 20756579. The reversal of 20756561 is 16565702.

It is a happy number.

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, and also an emirpimes, since its reverse is a distinct semiprime: 16565702 = 2 ⋅8282851.

It is a cyclic number.

It is not a de Polignac number, because 20756561 - 2¹⁴ = 20740177 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20756521) 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, 1482605 + ... + 1482618.

It is an arithmetic number, because the mean of its divisors is an integer number (5930448).

Almost surely, 2^20756561 is an apocalyptic number.

It is an amenable number.

20756561 is a deficient number, since it is larger than the sum of its proper divisors (2965231).

20756561 is an equidigital number, since it uses as much as digits as its factorization.

20756561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2965230.

The product of its (nonzero) digits is 12600, while the sum is 32.

The square root of 20756561 is about 4555.9368959633. The cubic root of 20756561 is about 274.8221924973.

The spelling of 20756561 in words is "twenty million, seven hundred fifty-six thousand, five hundred sixty-one".