661583640 has 64 divisors (see below), whose sum is σ = 2000424960. Its totient is φ = 175029120.

The previous prime is 661583623. The next prime is 661583647. The reversal of 661583640 is 46385166.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661583647) 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, 6466 + ... + 36945.

It is an arithmetic number, because the mean of its divisors is an integer number (31256640).

Almost surely, 2^661583640 is an apocalyptic number.

661583640 is a gapful number since it is divisible by the number (60) 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 661583640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1000212480).

661583640 is an abundant number, since it is smaller than the sum of its proper divisors (1338841320).

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

661583640 is a wasteful number, since it uses less digits than its factorization.

661583640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43552 (or 43548 counting only the distinct ones).

The product of its (nonzero) digits is 103680, while the sum is 39.

The square root of 661583640 is about 25721.2682424487. The cubic root of 661583640 is about 871.3545816040.

The spelling of 661583640 in words is "six hundred sixty-one million, five hundred eighty-three thousand, six hundred forty".