20861251909 has 4 divisors (see below), whose sum is σ = 20861699040. Its totient is φ = 20860804780.

The previous prime is 20861251907. The next prime is 20861251927. The reversal of 20861251909 is 90915216802.

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 a cyclic number.

It is not a de Polignac number, because 20861251909 - 2¹ = 20861251907 is a prime.

It is a super-2 number, since 2×20861251909² (a number of 21 digits) 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 (20861251907) 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, 144187 + ... + 250024.

It is an arithmetic number, because the mean of its divisors is an integer number (5215424760).

Almost surely, 2^20861251909 is an apocalyptic number.

It is an amenable number.

20861251909 is a deficient number, since it is larger than the sum of its proper divisors (447131).

20861251909 is an equidigital number, since it uses as much as digits as its factorization.

20861251909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 447130.

The product of its (nonzero) digits is 77760, while the sum is 43.

The spelling of 20861251909 in words is "twenty billion, eight hundred sixty-one million, two hundred fifty-one thousand, nine hundred nine".