21207956817 has 16 divisors (see below), whose sum is σ = 29613271680. Its totient is φ = 13475079552.

The previous prime is 21207956767. The next prime is 21207956821. The reversal of 21207956817 is 71865970212.

It is not a de Polignac number, because 21207956817 - 2²² = 21203762513 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21207956017) 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, 535692 + ... + 573917.

It is an arithmetic number, because the mean of its divisors is an integer number (1850829480).

Almost surely, 2^21207956817 is an apocalyptic number.

It is an amenable number.

21207956817 is a deficient number, since it is larger than the sum of its proper divisors (8405314863).

21207956817 is a wasteful number, since it uses less digits than its factorization.

21207956817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1109912.

The product of its (nonzero) digits is 423360, while the sum is 48.

The spelling of 21207956817 in words is "twenty-one billion, two hundred seven million, nine hundred fifty-six thousand, eight hundred seventeen".