661204534024021 has 4 divisors (see below), whose sum is σ = 712066421256652. Its totient is φ = 610342646791392.

The previous prime is 661204534024007. The next prime is 661204534024087. The reversal of 661204534024021 is 120420435402166.

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 109025548740900 + 552178985283121 = 10441530^2 + 23498489^2 .

It is a cyclic number.

It is not a de Polignac number, because 661204534024021 - 2¹³ = 661204534015829 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 (661204534024421) 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, 25430943616296 + ... + 25430943616321.

It is an arithmetic number, because the mean of its divisors is an integer number (178016605314163).

Almost surely, 2^{661204534024021} is an apocalyptic number.

It is an amenable number.

661204534024021 is a deficient number, since it is larger than the sum of its proper divisors (50861887232631).

661204534024021 is a wasteful number, since it uses less digits than its factorization.

661204534024021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50861887232630.

The product of its (nonzero) digits is 276480, while the sum is 40.

Adding to 661204534024021 its reverse (120420435402166), we get a palindrome (781624969426187).

The spelling of 661204534024021 in words is "six hundred sixty-one trillion, two hundred four billion, five hundred thirty-four million, twenty-four thousand, twenty-one".