661491305280 has 336 divisors, whose sum is σ = 2461005827280. Its totient is φ = 162115485696.

The previous prime is 661491305273. The next prime is 661491305303. The reversal of 661491305280 is 82503194166.

661491305280 is a `hidden beast` number, since 6 + 6 + 1 + 4 + 91 + 30 + 528 + 0 = 666.

It can be written as a sum of positive squares in 8 ways, for example, as 9583626816 + 651907678464 = 97896^2 + 807408^2 .

It is a super-2 number, since 2×661491305280² (a number of 24 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 8535184 + ... + 8612336.

It is an arithmetic number, because the mean of its divisors is an integer number (7324422105).

Almost surely, 2^661491305280 is an apocalyptic number.

661491305280 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 661491305280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1230502913640).

661491305280 is an abundant number, since it is smaller than the sum of its proper divisors (1799514522000).

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

661491305280 is a wasteful number, since it uses less digits than its factorization.

661491305280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 77418 (or 77405 counting only the distinct ones).

The product of its (nonzero) digits is 311040, while the sum is 45.

The spelling of 661491305280 in words is "six hundred sixty-one billion, four hundred ninety-one million, three hundred five thousand, two hundred eighty".