20406561 has 32 divisors (see below), whose sum is σ = 32272128. Its totient is φ = 11228160.

The previous prime is 20406559. The next prime is 20406563. The reversal of 20406561 is 16560402.

It is an interprime number because it is at equal distance from previous prime (20406559) and next prime (20406563).

It is not a de Polignac number, because 20406561 - 2¹ = 20406559 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20406563) 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 31 ways as a sum of consecutive naturals, for example, 117871 + ... + 118043.

It is an arithmetic number, because the mean of its divisors is an integer number (1008504).

Almost surely, 2^20406561 is an apocalyptic number.

20406561 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

20406561 is a deficient number, since it is larger than the sum of its proper divisors (11865567).

20406561 is a wasteful number, since it uses less digits than its factorization.

20406561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 361.

The product of its (nonzero) digits is 1440, while the sum is 24.

The square root of 20406561 is about 4517.3621727730. The cubic root of 20406561 is about 273.2687313451.

Adding to 20406561 its reverse (16560402), we get a palindrome (36966963).

The spelling of 20406561 in words is "twenty million, four hundred six thousand, five hundred sixty-one".