21554433445661 has 2 divisors, whose sum is σ = 21554433445662. Its totient is φ = 21554433445660.

The previous prime is 21554433445487. The next prime is 21554433445667. The reversal of 21554433445661 is 16654433445512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10845864409636 + 10708569036025 = 3293306^2 + 3272395^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21554433445661 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21554433445667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10777216722830 + 10777216722831.

It is an arithmetic number, because the mean of its divisors is an integer number (10777216722831).

Almost surely, 2^{21554433445661} is an apocalyptic number.

It is an amenable number.

21554433445661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21554433445661 is an equidigital number, since it uses as much as digits as its factorization.

21554433445661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20736000, while the sum is 53.

The spelling of 21554433445661 in words is "twenty-one trillion, five hundred fifty-four billion, four hundred thirty-three million, four hundred forty-five thousand, six hundred sixty-one".