21756256465 has 16 divisors (see below), whose sum is σ = 26609784336. Its totient is φ = 17070393600.

The previous prime is 21756256433. The next prime is 21756256469. The reversal of 21756256465 is 56465265712.

It can be written as a sum of positive squares in 8 ways, for example, as 5673704976 + 16082551489 = 75324^2 + 126817^2 .

It is not a de Polignac number, because 21756256465 - 2⁵ = 21756256433 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21756256469) 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, 797755 + ... + 824575.

It is an arithmetic number, because the mean of its divisors is an integer number (1663111521).

Almost surely, 2^21756256465 is an apocalyptic number.

It is an amenable number.

21756256465 is a deficient number, since it is larger than the sum of its proper divisors (4853527871).

21756256465 is a wasteful number, since it uses less digits than its factorization.

21756256465 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29940.

The product of its digits is 3024000, while the sum is 49.

The spelling of 21756256465 in words is "twenty-one billion, seven hundred fifty-six million, two hundred fifty-six thousand, four hundred sixty-five".