25815397781 has 4 divisors (see below), whose sum is σ = 26302480812. Its totient is φ = 25328314752.

The previous prime is 25815397757. The next prime is 25815397789. The reversal of 25815397781 is 18779351852.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 15862143025 + 9953254756 = 125945^2 + 99766^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-25815397781 is a prime.

It is a super-2 number, since 2×25815397781² (a number of 22 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (25815397789) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 243541436 + ... + 243541541.

It is an arithmetic number, because the mean of its divisors is an integer number (6575620203).

Almost surely, 2^25815397781 is an apocalyptic number.

It is an amenable number.

25815397781 is a deficient number, since it is larger than the sum of its proper divisors (487083031).

25815397781 is an equidigital number, since it uses as much as digits as its factorization.

25815397781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 487083030.

The product of its digits is 4233600, while the sum is 56.

The spelling of 25815397781 in words is "twenty-five billion, eight hundred fifteen million, three hundred ninety-seven thousand, seven hundred eighty-one".