661596721536 has 128 divisors (see below), whose sum is σ = 1865388411360. Its totient is φ = 207041331200.

The previous prime is 661596721531. The next prime is 661596721579. The reversal of 661596721536 is 635127695166.

It is a tau number, because it is divible by the number of its divisors (128).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661596721531) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2491360 + ... + 2744096.

Almost surely, 2^661596721536 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661596721536, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (932694205680).

661596721536 is an abundant number, since it is smaller than the sum of its proper divisors (1203791689824).

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

661596721536 is a wasteful number, since it uses less digits than its factorization.

661596721536 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 253172 (or 253160 counting only the distinct ones).

The product of its digits is 12247200, while the sum is 57.

The spelling of 661596721536 in words is "six hundred sixty-one billion, five hundred ninety-six million, seven hundred twenty-one thousand, five hundred thirty-six".