661155840 has 312 divisors, whose sum is σ = 2438034768. Its totient is φ = 165150720.

The previous prime is 661155811. The next prime is 661155851. The reversal of 661155840 is 48551166.

661155840 is a `hidden beast` number, since 6 + 61 + 1 + 558 + 40 = 666.

It is a super-2 number, since 2×661155840² = 874254089532211200, which contains 22 as substring.

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

It is a junction number, because it is equal to n+sod(n) for n = 661155795 and 661155804.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3133335 + ... + 3133545.

It is an arithmetic number, because the mean of its divisors is an integer number (7814214).

Almost surely, 2^661155840 is an apocalyptic number.

661155840 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 661155840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1219017384).

661155840 is an abundant number, since it is smaller than the sum of its proper divisors (1776878928).

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

661155840 is a wasteful number, since it uses less digits than its factorization.

661155840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 263 (or 238 counting only the distinct ones).

The product of its (nonzero) digits is 28800, while the sum is 36.

The square root of 661155840 is about 25712.9508224941. The cubic root of 661155840 is about 871.1667263611.

The spelling of 661155840 in words is "six hundred sixty-one million, one hundred fifty-five thousand, eight hundred forty".