661357775540 has 144 divisors (see below), whose sum is σ = 1780280544000. Its totient is φ = 206137229760.

The previous prime is 661357775473. The next prime is 661357775587. The reversal of 661357775540 is 45577753166.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 431681 + ... + 1228439.

Almost surely, 2^661357775540 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 661357775540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (890140272000).

661357775540 is an abundant number, since it is smaller than the sum of its proper divisors (1118922768460).

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

661357775540 is a wasteful number, since it uses less digits than its factorization.

661357775540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 796811 (or 796784 counting only the distinct ones).

The product of its (nonzero) digits is 18522000, while the sum is 56.

The spelling of 661357775540 in words is "six hundred sixty-one billion, three hundred fifty-seven million, seven hundred seventy-five thousand, five hundred forty".