20409661 has 4 divisors (see below), whose sum is σ = 20424924. Its totient is φ = 20394400.

The previous prime is 20409643. The next prime is 20409679. The reversal of 20409661 is 16690402.

20409661 = 3194² + 3195².

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (20409643) and next prime (20409679).

It can be written as a sum of positive squares in 2 ways, for example, as 10201636 + 10208025 = 3194^2 + 3195^2 .

It is a cyclic number.

It is not a de Polignac number, because 20409661 - 2⁹ = 20409149 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20409601) 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, 5410 + ... + 8371.

It is an arithmetic number, because the mean of its divisors is an integer number (5106231).

Almost surely, 2^20409661 is an apocalyptic number.

20409661 is the 3195-th centered square number.

It is an amenable number.

20409661 is a deficient number, since it is larger than the sum of its proper divisors (15263).

20409661 is a wasteful number, since it uses less digits than its factorization.

20409661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15262.

The product of its (nonzero) digits is 2592, while the sum is 28.

The square root of 20409661 is about 4517.7052803387. The cubic root of 20409661 is about 273.2825682376.

The spelling of 20409661 in words is "twenty million, four hundred nine thousand, six hundred sixty-one".