21661246561543 has 2 divisors, whose sum is σ = 21661246561544. Its totient is φ = 21661246561542.

The previous prime is 21661246561531. The next prime is 21661246561597. The reversal of 21661246561543 is 34516564216612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21661246561543 - 2⁴¹ = 19462223305991 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21661246531543) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830623280771 + 10830623280772.

It is an arithmetic number, because the mean of its divisors is an integer number (10830623280772).

Almost surely, 2^{21661246561543} is an apocalyptic number.

21661246561543 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661246561543 is an equidigital number, since it uses as much as digits as its factorization.

21661246561543 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6220800, while the sum is 52.

The spelling of 21661246561543 in words is "twenty-one trillion, six hundred sixty-one billion, two hundred forty-six million, five hundred sixty-one thousand, five hundred forty-three".