20403561 has 4 divisors (see below), whose sum is σ = 27204752. Its totient is φ = 13602372.

The previous prime is 20403541. The next prime is 20403589. The reversal of 20403561 is 16530402.

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.

It is not a de Polignac number, because 20403561 - 2¹⁰ = 20402537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20403521) 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, 3400591 + ... + 3400596.

It is an arithmetic number, because the mean of its divisors is an integer number (6801188).

Almost surely, 2^20403561 is an apocalyptic number.

It is an amenable number.

20403561 is a deficient number, since it is larger than the sum of its proper divisors (6801191).

20403561 is an equidigital number, since it uses as much as digits as its factorization.

20403561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6801190.

The product of its (nonzero) digits is 720, while the sum is 21.

The square root of 20403561 is about 4517.0301083787. The cubic root of 20403561 is about 273.2553394696.

Adding to 20403561 its reverse (16530402), we get a palindrome (36933963).

The spelling of 20403561 in words is "twenty million, four hundred three thousand, five hundred sixty-one".