20766561 has 4 divisors (see below), whose sum is σ = 27688752. Its totient is φ = 13844372.

The previous prime is 20766533. The next prime is 20766593. The reversal of 20766561 is 16566702.

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 20766561 - 2¹⁸ = 20504417 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20766521) 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, 3461091 + ... + 3461096.

It is an arithmetic number, because the mean of its divisors is an integer number (6922188).

Almost surely, 2^20766561 is an apocalyptic number.

It is an amenable number.

20766561 is a deficient number, since it is larger than the sum of its proper divisors (6922191).

20766561 is an equidigital number, since it uses as much as digits as its factorization.

20766561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6922190.

The product of its (nonzero) digits is 15120, while the sum is 33.

The square root of 20766561 is about 4557.0342329195. The cubic root of 20766561 is about 274.8663196001.

The spelling of 20766561 in words is "twenty million, seven hundred sixty-six thousand, five hundred sixty-one".