21720201855 has 32 divisors (see below), whose sum is σ = 38184410880. Its totient is φ = 10455233280.

The previous prime is 21720201851. The next prime is 21720201859. The reversal of 21720201855 is 55810202712.

It is an interprime number because it is at equal distance from previous prime (21720201851) and next prime (21720201859).

It is not a de Polignac number, because 21720201855 - 2² = 21720201851 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720201851) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 450582 + ... + 496451.

It is an arithmetic number, because the mean of its divisors is an integer number (1193262840).

Almost surely, 2^21720201855 is an apocalyptic number.

21720201855 is a deficient number, since it is larger than the sum of its proper divisors (16464209025).

21720201855 is a wasteful number, since it uses less digits than its factorization.

21720201855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 947191.

The product of its (nonzero) digits is 11200, while the sum is 33.

The spelling of 21720201855 in words is "twenty-one billion, seven hundred twenty million, two hundred one thousand, eight hundred fifty-five".