20402561 has 4 divisors (see below), whose sum is σ = 21476400. Its totient is φ = 19328724.

The previous prime is 20402537. The next prime is 20402563. The reversal of 20402561 is 16520402.

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: 16520402 = 2 ⋅8260201.

It is a cyclic number.

It is not a de Polignac number, because 20402561 - 2⁶ = 20402497 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (20402563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 536891 + ... + 536928.

It is an arithmetic number, because the mean of its divisors is an integer number (5369100).

Almost surely, 2^20402561 is an apocalyptic number.

It is an amenable number.

20402561 is a deficient number, since it is larger than the sum of its proper divisors (1073839).

20402561 is a wasteful number, since it uses less digits than its factorization.

20402561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1073838.

The product of its (nonzero) digits is 480, while the sum is 20.

The square root of 20402561 is about 4516.9194148225. The cubic root of 20402561 is about 273.2508752194.

Adding to 20402561 its reverse (16520402), we get a palindrome (36922963).

The spelling of 20402561 in words is "twenty million, four hundred two thousand, five hundred sixty-one".