661307251264 has 63 divisors (see below), whose sum is σ = 1442581310793. Its totient is φ = 300561676800.

The previous prime is 661307251207. The next prime is 661307251277. The reversal of 661307251264 is 462152703166.

The square root of 661307251264 is 813208.

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

It can be written as a sum of positive squares in only one way, i.e., 654170380864 + 7136870400 = 808808^2 + 84480^2 .

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 661307251264.

It is an unprimeable number.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 71557684 + ... + 71566924.

Almost surely, 2^661307251264 is an apocalyptic number.

661307251264 is a gapful number since it is divisible by the number (64) formed by its first and last digit.

661307251264 is the 813208-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661307251264

661307251264 is an abundant number, since it is smaller than the sum of its proper divisors (781274059529).

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

661307251264 is an frugal number, since it uses more digits than its factorization.

661307251264 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18516 (or 9254 counting only the distinct ones).

The product of its (nonzero) digits is 362880, while the sum is 43.

The spelling of 661307251264 in words is "six hundred sixty-one billion, three hundred seven million, two hundred fifty-one thousand, two hundred sixty-four".