661975856640 has 1920 divisors, whose sum is σ = 2937754828800. Its totient is φ = 142216445952.

The previous prime is 661975856623. The next prime is 661975856657. The reversal of 661975856640 is 46658579166.

661975856640 is a `hidden beast` number, since 6 + 6 + 1 + 9 + 7 + 585 + 6 + 6 + 40 = 666.

It is an interprime number because it is at equal distance from previous prime (661975856623) and next prime (661975856657).

It is a tau number, because it is divible by the number of its divisors (1920).

It is a Harshad number since it is a multiple of its sum of digits (63).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 191 ways as a sum of consecutive naturals, for example, 5212408257 + ... + 5212408383.

It is an arithmetic number, because the mean of its divisors is an integer number (1530080640).

Almost surely, 2^661975856640 is an apocalyptic number.

661975856640 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 661975856640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1468877414400).

661975856640 is an abundant number, since it is smaller than the sum of its proper divisors (2275778972160).

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

661975856640 is an equidigital number, since it uses as much as digits as its factorization.

661975856640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 204 (or 163 counting only the distinct ones).

The product of its (nonzero) digits is 65318400, while the sum is 63.

The spelling of 661975856640 in words is "six hundred sixty-one billion, nine hundred seventy-five million, eight hundred fifty-six thousand, six hundred forty".