661326768400 has 135 divisors (see below), whose sum is σ = 1613797902381. Its totient is φ = 260438584320.

The previous prime is 661326768397. The next prime is 661326768419. The reversal of 661326768400 is 4867623166.

The square root of 661326768400 is 813220.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 13 ways, for example, as 627916777744 + 33409990656 = 792412^2 + 182784^2 .

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 1187300922 + ... + 1187301478.

Almost surely, 2^661326768400 is an apocalyptic number.

661326768400 is the 813220-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661326768400

661326768400 is an abundant number, since it is smaller than the sum of its proper divisors (952471133981).

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

661326768400 is an frugal number, since it uses more digits than its factorization.

661326768400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1278 (or 637 counting only the distinct ones).

The product of its (nonzero) digits is 1741824, while the sum is 49.

Multiplying 661326768400 by its sum of digits (49), we get a square (32405011651600 = 5692540²).

The spelling of 661326768400 in words is "six hundred sixty-one billion, three hundred twenty-six million, seven hundred sixty-eight thousand, four hundred".