20720856687409 has 4 divisors (see below), whose sum is σ = 20721076731904. Its totient is φ = 20720636642916.

The previous prime is 20720856687389. The next prime is 20720856687437. The reversal of 20720856687409 is 90478665802702.

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 20720856687409 - 2⁷ = 20720856687281 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20720856688409) 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, 109880937 + ... + 110069350.

It is an arithmetic number, because the mean of its divisors is an integer number (5180269182976).

Almost surely, 2^{20720856687409} is an apocalyptic number.

It is an amenable number.

20720856687409 is a deficient number, since it is larger than the sum of its proper divisors (220044495).

20720856687409 is an equidigital number, since it uses as much as digits as its factorization.

20720856687409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 220044494.

The product of its (nonzero) digits is 81285120, while the sum is 64.

The spelling of 20720856687409 in words is "twenty trillion, seven hundred twenty billion, eight hundred fifty-six million, six hundred eighty-seven thousand, four hundred nine".