661626312520 has 16 divisors (see below), whose sum is σ = 1488659203260. Its totient is φ = 264650524992.

The previous prime is 661626312511. The next prime is 661626312521. The reversal of 661626312520 is 25213626166.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 647564621796 + 14061690724 = 804714^2 + 118582^2 .

It is a Harshad number since it is a multiple of its sum of digits (40), and also a Moran number because the ratio is a prime number: 16540657813 = 661626312520 / (6 + 6 + 1 + 6 + 2 + 6 + 3 + 1 + 2 + 5 + 2 + 0).

It is not an unprimeable number, because it can be changed into a prime (661626312521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8270328867 + ... + 8270328946.

Almost surely, 2^661626312520 is an apocalyptic number.

It is an amenable number.

661626312520 is an abundant number, since it is smaller than the sum of its proper divisors (827032890740).

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

661626312520 is a wasteful number, since it uses less digits than its factorization.

661626312520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16540657824 (or 16540657820 counting only the distinct ones).

The product of its (nonzero) digits is 155520, while the sum is 40.

Adding to 661626312520 its reverse (25213626166), we get a palindrome (686839938686).

The spelling of 661626312520 in words is "six hundred sixty-one billion, six hundred twenty-six million, three hundred twelve thousand, five hundred twenty".