661238081280 has 648 divisors, whose sum is σ = 2726341725744. Its totient is φ = 147448627200.

The previous prime is 661238081249. The next prime is 661238081281. The reversal of 661238081280 is 82180832166.

661238081280 is a `hidden beast` number, since 6 + 61 + 238 + 0 + 81 + 280 = 666.

It is a hoax number, since the sum of its digits (45) coincides with the sum of the digits of its distinct prime factors.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661238081281) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 23129395 + ... + 23157965.

It is an arithmetic number, because the mean of its divisors is an integer number (4207317478).

Almost surely, 2^661238081280 is an apocalyptic number.

661238081280 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 661238081280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1363170862872).

661238081280 is an abundant number, since it is smaller than the sum of its proper divisors (2065103644464).

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

661238081280 is a wasteful number, since it uses less digits than its factorization.

661238081280 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28653 (or 28629 counting only the distinct ones).

The product of its (nonzero) digits is 221184, while the sum is 45.

The spelling of 661238081280 in words is "six hundred sixty-one billion, two hundred thirty-eight million, eighty-one thousand, two hundred eighty".