81526778649 has 12 divisors (see below), whose sum is σ = 117764440612. Its totient is φ = 54349552800.

The previous prime is 81526778647. The next prime is 81526778681. The reversal of 81526778649 is 94687762518.

It can be written as a sum of positive squares in 2 ways, for example, as 48910418649 + 32616360000 = 221157^2 + 180600^2 .

It is not a de Polignac number, because 81526778649 - 2¹ = 81526778647 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81526778647) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 232719 + ... + 466059.

Almost surely, 2^81526778649 is an apocalyptic number.

It is an amenable number.

81526778649 is a deficient number, since it is larger than the sum of its proper divisors (36237661963).

81526778649 is a wasteful number, since it uses less digits than its factorization.

81526778649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 272168 (or 272165 counting only the distinct ones).

The product of its digits is 40642560, while the sum is 63.

The spelling of 81526778649 in words is "eighty-one billion, five hundred twenty-six million, seven hundred seventy-eight thousand, six hundred forty-nine".