21506065664465 has 16 divisors (see below), whose sum is σ = 27334143470160. Its totient is φ = 16187593820160.

The previous prime is 21506065664453. The next prime is 21506065664467. The reversal of 21506065664465 is 56446656060512.

21506065664465 is digitally balanced in base 6, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 8 ways, for example, as 1547625569296 + 19958440095169 = 1244036^2 + 4467487^2 .

It is not a de Polignac number, because 21506065664465 - 2²² = 21506061470161 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21506065664465.

It is not an unprimeable number, because it can be changed into a prime (21506065664467) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 40426076 + ... + 40954605.

It is an arithmetic number, because the mean of its divisors is an integer number (1708383966885).

Almost surely, 2^{21506065664465} is an apocalyptic number.

It is an amenable number.

21506065664465 is a deficient number, since it is larger than the sum of its proper divisors (5828077805695).

21506065664465 is a wasteful number, since it uses less digits than its factorization.

21506065664465 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 81383812.

The product of its (nonzero) digits is 31104000, while the sum is 56.

The spelling of 21506065664465 in words is "twenty-one trillion, five hundred six billion, sixty-five million, six hundred sixty-four thousand, four hundred sixty-five".