20561691 has 8 divisors (see below), whose sum is σ = 27791440. Its totient is φ = 13519872.

The previous prime is 20561689. The next prime is 20561693. The reversal of 20561691 is 19616502.

It is an interprime number because it is at equal distance from previous prime (20561689) and next prime (20561693).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 20561691 - 2¹ = 20561689 is a prime.

It is the 4535-th Hogben number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20561693) by changing a digit.

It is a nontrivial repunit in base 4534.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 46726 + ... + 47163.

It is an arithmetic number, because the mean of its divisors is an integer number (3473930).

Almost surely, 2^20561691 is an apocalyptic number.

20561691 is a deficient number, since it is larger than the sum of its proper divisors (7229749).

20561691 is an equidigital number, since it uses as much as digits as its factorization.

20561691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 93965.

The product of its (nonzero) digits is 3240, while the sum is 30.

The square root of 20561691 is about 4534.5000826993. The cubic root of 20561691 is about 273.9594439770.

The spelling of 20561691 in words is "twenty million, five hundred sixty-one thousand, six hundred ninety-one".