1638720720 has 600 divisors, whose sum is σ = 7147995624. Its totient is φ = 344881152.

The previous prime is 1638720703. The next prime is 1638720757. The reversal of 1638720720 is 270278361.

It can be written as a sum of positive squares in 4 ways, for example, as 73410624 + 1565310096 = 8568^2 + 39564^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 119 ways as a sum of consecutive naturals, for example, 4127562 + ... + 4127958.

Almost surely, 2^1638720720 is an apocalyptic number.

1638720720 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1638720720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3573997812).

1638720720 is an abundant number, since it is smaller than the sum of its proper divisors (5509274904).

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

1638720720 is a wasteful number, since it uses less digits than its factorization.

1638720720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 449 (or 427 counting only the distinct ones).

The product of its (nonzero) digits is 28224, while the sum is 36.

The square root of 1638720720 is about 40481.1155972757. The cubic root of 1638720720 is about 1178.9669978914.

The spelling of 1638720720 in words is "one billion, six hundred thirty-eight million, seven hundred twenty thousand, seven hundred twenty".