20715561 has 8 divisors (see below), whose sum is σ = 30689760. Its totient is φ = 13810356.

The previous prime is 20715557. The next prime is 20715577. The reversal of 20715561 is 16551702.

It is not a de Polignac number, because 20715561 - 2² = 20715557 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 767243 = 20715561 / (2 + 0 + 7 + 1 + 5 + 5 + 6 + 1).

It is not an unprimeable number, because it can be changed into a prime (20715581) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 383595 + ... + 383648.

It is an arithmetic number, because the mean of its divisors is an integer number (3836220).

Almost surely, 2^20715561 is an apocalyptic number.

It is an amenable number.

20715561 is a deficient number, since it is larger than the sum of its proper divisors (9974199).

20715561 is an equidigital number, since it uses as much as digits as its factorization.

20715561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 767252 (or 767246 counting only the distinct ones).

The product of its (nonzero) digits is 2100, while the sum is 27.

The square root of 20715561 is about 4551.4350484215. The cubic root of 20715561 is about 274.6411230513.

The spelling of 20715561 in words is "twenty million, seven hundred fifteen thousand, five hundred sixty-one".