661309440 has 384 divisors, whose sum is σ = 2453068800. Its totient is φ = 150405120.

The previous prime is 661309403. The next prime is 661309457. The reversal of 661309440 is 44903166.

It is a tau number, because it is divible by the number of its divisors (384).

It is a super-2 number, since 2×661309440² = 874660350866227200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 6420429 + ... + 6420531.

It is an arithmetic number, because the mean of its divisors is an integer number (6388200).

Almost surely, 2^661309440 is an apocalyptic number.

661309440 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 661309440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1226534400).

661309440 is an abundant number, since it is smaller than the sum of its proper divisors (1791759360).

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

661309440 is a wasteful number, since it uses less digits than its factorization.

661309440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 163 (or 143 counting only the distinct ones).

The product of its (nonzero) digits is 15552, while the sum is 33.

The square root of 661309440 is about 25715.9374707593. The cubic root of 661309440 is about 871.2341844096.

The spelling of 661309440 in words is "six hundred sixty-one million, three hundred nine thousand, four hundred forty".