21661246561643 has 16 divisors (see below), whose sum is σ = 23373229130496. Its totient is φ = 19955800962720.

The previous prime is 21661246561609. The next prime is 21661246561651. The reversal of 21661246561643 is 34616564216612.

It is a cyclic number.

It is not a de Polignac number, because 21661246561643 - 2¹⁶ = 21661246496107 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21661246561543) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 167401496 + ... + 167530842.

It is an arithmetic number, because the mean of its divisors is an integer number (1460826820656).

Almost surely, 2^{21661246561643} is an apocalyptic number.

21661246561643 is a deficient number, since it is larger than the sum of its proper divisors (1711982568853).

21661246561643 is a wasteful number, since it uses less digits than its factorization.

21661246561643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 154514.

The product of its digits is 7464960, while the sum is 53.

The spelling of 21661246561643 in words is "twenty-one trillion, six hundred sixty-one billion, two hundred forty-six million, five hundred sixty-one thousand, six hundred forty-three".