81777664 has 22 divisors (see below), whose sum is σ = 163477514. Its totient is φ = 40888320.

The previous prime is 81777649. The next prime is 81777671. The reversal of 81777664 is 46677718.

It can be written as a sum of positive squares in only one way, i.e., 80856064 + 921600 = 8992^2 + 960^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 38907 + ... + 40954.

Almost surely, 2^81777664 is an apocalyptic number.

It is an amenable number.

81777664 is a deficient number, since it is larger than the sum of its proper divisors (81699850).

81777664 is an equidigital number, since it uses as much as digits as its factorization.

81777664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 79881 (or 79863 counting only the distinct ones).

The product of its digits is 395136, while the sum is 46.

The square root of 81777664 is about 9043.1003533080. The cubic root of 81777664 is about 434.0551368006.

The spelling of 81777664 in words is "eighty-one million, seven hundred seventy-seven thousand, six hundred sixty-four".