1661643640 has 64 divisors (see below), whose sum is σ = 3832012800. Its totient is φ = 648171648.

The previous prime is 1661643623. The next prime is 1661643647. The reversal of 1661643640 is 463461661.

It is a super-2 number, since 2×1661643640² = 5522119172704899200, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 1661643640.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661643647) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 575721 + ... + 578599.

It is an arithmetic number, because the mean of its divisors is an integer number (59875200).

Almost surely, 2^1661643640 is an apocalyptic number.

1661643640 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 1661643640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1916006400).

1661643640 is an abundant number, since it is smaller than the sum of its proper divisors (2170369160).

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

1661643640 is a wasteful number, since it uses less digits than its factorization.

1661643640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3244 (or 3240 counting only the distinct ones).

The product of its (nonzero) digits is 62208, while the sum is 37.

The square root of 1661643640 is about 40763.2633629841. The cubic root of 1661643640 is about 1184.4388115845.

The spelling of 1661643640 in words is "one billion, six hundred sixty-one million, six hundred forty-three thousand, six hundred forty".