21311620225 has 81 divisors (see below), whose sum is σ = 31800259017. Its totient is φ = 14126676480.

The previous prime is 21311620177. The next prime is 21311620229. The reversal of 21311620225 is 52202611312.

The square root of 21311620225 is 145985.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 783608049 + 20528012176 = 27993^2 + 143276^2 .

It is not a de Polignac number, because 21311620225 - 2¹³ = 21311612033 is a prime.

It is a super-2 number, since 2×21311620225² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (25).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21311620225.

It is not an unprimeable number, because it can be changed into a prime (21311620229) by changing a digit.

It is a polite number, since it can be written in 80 ways as a sum of consecutive naturals, for example, 219707377 + ... + 219707473.

Almost surely, 2^21311620225 is an apocalyptic number.

21311620225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21311620225 is the 145985-th square number.

21311620225 is the 72993-rd centered octagonal number.

It is an amenable number.

21311620225 is a deficient number, since it is larger than the sum of its proper divisors (10488638792).

21311620225 is an frugal number, since it uses more digits than its factorization.

21311620225 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 304 (or 152 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 25.

Multiplying 21311620225 by its sum of digits (25), we get a square (532790505625 = 729925²).

21311620225 divided by its sum of digits (25) gives a square (852464809 = 29197²).

The spelling of 21311620225 in words is "twenty-one billion, three hundred eleven million, six hundred twenty thousand, two hundred twenty-five".