661026816 has 72 divisors (see below), whose sum is σ = 1909220040. Its totient is φ = 220336128.

The previous prime is 661026799. The next prime is 661026829. The reversal of 661026816 is 618620166.

661026816 is a `hidden beast` number, since 6 + 610 + 26 + 8 + 16 = 666.

It is a tau number, because it is divible by the number of its divisors (72).

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 501 + ... + 36363.

It is an arithmetic number, because the mean of its divisors is an integer number (26516945).

Almost surely, 2^661026816 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 661026816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (954610020).

661026816 is an abundant number, since it is smaller than the sum of its proper divisors (1248193224).

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

661026816 is a wasteful number, since it uses less digits than its factorization.

661026816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35891 (or 35868 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 36.

The square root of 661026816 is about 25710.4417698335. The cubic root of 661026816 is about 871.1100535258.

The spelling of 661026816 in words is "six hundred sixty-one million, twenty-six thousand, eight hundred sixteen".