20409581 has 4 divisors (see below), whose sum is σ = 20419872. Its totient is φ = 20399292.

The previous prime is 20409547. The next prime is 20409583. The reversal of 20409581 is 18590402.

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 a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 18590402 = 2 ⋅9295201.

It is a cyclic number.

It is not a de Polignac number, because 20409581 - 2¹⁸ = 20147437 is a prime.

It is a super-2 number, since 2×20409581² = 833101993191122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20409583) 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, 1121 + ... + 6486.

It is an arithmetic number, because the mean of its divisors is an integer number (5104968).

Almost surely, 2^20409581 is an apocalyptic number.

It is an amenable number.

20409581 is a deficient number, since it is larger than the sum of its proper divisors (10291).

20409581 is an equidigital number, since it uses as much as digits as its factorization.

20409581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10290.

The product of its (nonzero) digits is 2880, while the sum is 29.

The square root of 20409581 is about 4517.6964262774. The cubic root of 20409581 is about 273.2822111741.

Adding to 20409581 its reverse (18590402), we get a palindrome (38999983).

The spelling of 20409581 in words is "twenty million, four hundred nine thousand, five hundred eighty-one".