77821640 has 64 divisors (see below), whose sum is σ = 190436400. Its totient is φ = 28449792.

The previous prime is 77821633. The next prime is 77821643. The reversal of 77821640 is 4612877.

It is a happy number.

It can be written as a sum of positive squares in 8 ways, for example, as 52157284 + 25664356 = 7222^2 + 5066^2 .

It is a hoax number, since the sum of its digits (35) coincides with the sum of the digits of its distinct prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 77821640.

It is not an unprimeable number, because it can be changed into a prime (77821643) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 55994 + ... + 57366.

Almost surely, 2^77821640 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 77821640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (95218200).

77821640 is an abundant number, since it is smaller than the sum of its proper divisors (112614760).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

77821640 is a wasteful number, since it uses less digits than its factorization.

77821640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1506 (or 1502 counting only the distinct ones).

The product of its (nonzero) digits is 18816, while the sum is 35.

The square root of 77821640 is about 8821.6574406401. The cubic root of 77821640 is about 426.9399480804.

The spelling of 77821640 in words is "seventy-seven million, eight hundred twenty-one thousand, six hundred forty".