661626331649 has 4 divisors (see below), whose sum is σ = 668447221764. Its totient is φ = 654805441536.

The previous prime is 661626331627. The next prime is 661626331651. The reversal of 661626331649 is 946133626166.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 526299466225 + 135326865424 = 725465^2 + 367868^2 .

It is a cyclic number.

It is not a de Polignac number, because 661626331649 - 2⁸ = 661626331393 is a prime.

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 661626331649.

It is not an unprimeable number, because it can be changed into a prime (661626331549) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3410444912 + ... + 3410445105.

It is an arithmetic number, because the mean of its divisors is an integer number (167111805441).

Almost surely, 2^661626331649 is an apocalyptic number.

It is an amenable number.

661626331649 is a deficient number, since it is larger than the sum of its proper divisors (6820890115).

661626331649 is an equidigital number, since it uses as much as digits as its factorization.

661626331649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6820890114.

The product of its digits is 5038848, while the sum is 53.

The spelling of 661626331649 in words is "six hundred sixty-one billion, six hundred twenty-six million, three hundred thirty-one thousand, six hundred forty-nine".