21720956409 has 16 divisors (see below), whose sum is σ = 32183399040. Its totient is φ = 14478745680.

The previous prime is 21720956381. The next prime is 21720956417. The reversal of 21720956409 is 90465902712.

21720956409 is a `hidden beast` number, since 217 + 20 + 9 + 5 + 6 + 409 = 666.

It is not a de Polignac number, because 21720956409 - 2⁹ = 21720955897 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21720956429) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 175999 + ... + 272795.

It is an arithmetic number, because the mean of its divisors is an integer number (2011462440).

Almost surely, 2^21720956409 is an apocalyptic number.

It is an amenable number.

21720956409 is a deficient number, since it is larger than the sum of its proper divisors (10462442631).

21720956409 is an equidigital number, since it uses as much as digits as its factorization.

21720956409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 105117 (or 105111 counting only the distinct ones).

The product of its (nonzero) digits is 272160, while the sum is 45.

The spelling of 21720956409 in words is "twenty-one billion, seven hundred twenty million, nine hundred fifty-six thousand, four hundred nine".