661121627021 has 4 divisors (see below), whose sum is σ = 661139624700. Its totient is φ = 661103629344.

The previous prime is 661121627003. The next prime is 661121627029. The reversal of 661121627021 is 120726121166.

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 529490530921 + 131631096100 = 727661^2 + 362810^2 .

It is a cyclic number.

It is not a de Polignac number, because 661121627021 - 2¹⁴ = 661121610637 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661121627029) 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, 8943626 + ... + 9017243.

It is an arithmetic number, because the mean of its divisors is an integer number (165284906175).

Almost surely, 2^661121627021 is an apocalyptic number.

It is an amenable number.

661121627021 is a deficient number, since it is larger than the sum of its proper divisors (17997679).

661121627021 is a wasteful number, since it uses less digits than its factorization.

661121627021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17997678.

The product of its (nonzero) digits is 12096, while the sum is 35.

Adding to 661121627021 its reverse (120726121166), we get a palindrome (781847748187).

The spelling of 661121627021 in words is "six hundred sixty-one billion, one hundred twenty-one million, six hundred twenty-seven thousand, twenty-one".