20861261909 has 4 divisors (see below), whose sum is σ = 20869874016. Its totient is φ = 20852649804.

The previous prime is 20861261857. The next prime is 20861261921. The reversal of 20861261909 is 90916216802.

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 an emirpimes, since its reverse is a distinct semiprime: 90916216802 = 2 ⋅45458108401.

It is a cyclic number.

It is not a de Polignac number, because 20861261909 - 2⁸ = 20861261653 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20861261909.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20861261989) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4302419 + ... + 4307264.

It is an arithmetic number, because the mean of its divisors is an integer number (5217468504).

Almost surely, 2^20861261909 is an apocalyptic number.

It is an amenable number.

20861261909 is a deficient number, since it is larger than the sum of its proper divisors (8612107).

20861261909 is an equidigital number, since it uses as much as digits as its factorization.

20861261909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8612106.

The product of its (nonzero) digits is 93312, while the sum is 44.

The spelling of 20861261909 in words is "twenty billion, eight hundred sixty-one million, two hundred sixty-one thousand, nine hundred nine".