12565440821 has 2 divisors, whose sum is σ = 12565440822. Its totient is φ = 12565440820.

The previous prime is 12565440781. The next prime is 12565440869. The reversal of 12565440821 is 12804456521.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12230148100 + 335292721 = 110590^2 + 18311^2 .

It is a cyclic number.

It is not a de Polignac number, because 12565440821 - 2²² = 12561246517 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (12565440721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 6282720410 + 6282720411.

It is an arithmetic number, because the mean of its divisors is an integer number (6282720411).

Almost surely, 2^12565440821 is an apocalyptic number.

It is an amenable number.

12565440821 is a deficient number, since it is larger than the sum of its proper divisors (1).

12565440821 is an equidigital number, since it uses as much as digits as its factorization.

12565440821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 76800, while the sum is 38.

The spelling of 12565440821 in words is "twelve billion, five hundred sixty-five million, four hundred forty thousand, eight hundred twenty-one".