20768561 has 6 divisors (see below), whose sum is σ = 22828386. Its totient is φ = 18880400.

The previous prime is 20768551. The next prime is 20768567. The reversal of 20768561 is 16586702.

20768561 = 164² + 165² + ... + 405².

It can be written as a sum of positive squares in only one way, i.e., 16120225 + 4648336 = 4015^2 + 2156^2 .

It is not a de Polignac number, because 20768561 - 2⁶ = 20768497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20768567) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 85700 + ... + 85941.

It is an arithmetic number, because the mean of its divisors is an integer number (3804731).

Almost surely, 2^20768561 is an apocalyptic number.

It is an amenable number.

20768561 is a deficient number, since it is larger than the sum of its proper divisors (2059825).

20768561 is a wasteful number, since it uses less digits than its factorization.

20768561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 171663 (or 171652 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 35.

The square root of 20768561 is about 4557.2536686035. The cubic root of 20768561 is about 274.8751433206.

The spelling of 20768561 in words is "twenty million, seven hundred sixty-eight thousand, five hundred sixty-one".