666621627961 has 3 divisors (see below), whose sum is σ = 666622444431. Its totient is φ = 666620811492.

The previous prime is 666621627913. The next prime is 666621627983. The reversal of 666621627961 is 169726126666.

It is a happy number.

The square root of 666621627961 is 816469.

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

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 3602280361 + 663019347600 = 60019^2 + 814260^2 .

It is not a de Polignac number, because 666621627961 - 2¹¹ = 666621625913 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 666621627896 and 666621627905.

It is not an unprimeable number, because it can be changed into a prime (666621667961) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 408235 + ... + 1224703.

It is an arithmetic number, because the mean of its divisors is an integer number (222207481477).

Almost surely, 2^666621627961 is an apocalyptic number.

666621627961 is the 816469-th square number.

666621627961 is the 408235-th centered octagonal number.

It is an amenable number.

666621627961 is a deficient number, since it is larger than the sum of its proper divisors (816470).

666621627961 is an frugal number, since it uses more digits than its factorization.

666621627961 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1632938 (or 816469 counting only the distinct ones).

The product of its digits is 11757312, while the sum is 58.

The spelling of 666621627961 in words is "six hundred sixty-six billion, six hundred twenty-one million, six hundred twenty-seven thousand, nine hundred sixty-one".