661511840 has 144 divisors (see below), whose sum is σ = 1756774656. Its totient is φ = 235107840.

The previous prime is 661511833. The next prime is 661511849. The reversal of 661511840 is 48115166.

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a junction number, because it is equal to n+sod(n) for n = 661511797 and 661511806.

It is not an unprimeable number, because it can be changed into a prime (661511849) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 909557 + ... + 910283.

It is an arithmetic number, because the mean of its divisors is an integer number (12199824).

Almost surely, 2^661511840 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 661511840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (878387328).

661511840 is an abundant number, since it is smaller than the sum of its proper divisors (1095262816).

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

661511840 is a wasteful number, since it uses less digits than its factorization.

661511840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 811 (or 792 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 32.

The square root of 661511840 is about 25719.8724724677. The cubic root of 661511840 is about 871.3230584936.

The spelling of 661511840 in words is "six hundred sixty-one million, five hundred eleven thousand, eight hundred forty".