661653452021 has 2 divisors, whose sum is σ = 661653452022. Its totient is φ = 661653452020.

The previous prime is 661653451997. The next prime is 661653452029. The reversal of 661653452021 is 120254356166.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 650845562500 + 10807889521 = 806750^2 + 103961^2 .

It is a cyclic number.

It is not a de Polignac number, because 661653452021 - 2¹⁴ = 661653435637 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 661653452021.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661653452029) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330826726010 + 330826726011.

It is an arithmetic number, because the mean of its divisors is an integer number (330826726011).

Almost surely, 2^661653452021 is an apocalyptic number.

It is an amenable number.

661653452021 is a deficient number, since it is larger than the sum of its proper divisors (1).

661653452021 is an equidigital number, since it uses as much as digits as its factorization.

661653452021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 259200, while the sum is 41.

The spelling of 661653452021 in words is "six hundred sixty-one billion, six hundred fifty-three million, four hundred fifty-two thousand, twenty-one".