21661042216643 has 2 divisors, whose sum is σ = 21661042216644. Its totient is φ = 21661042216642.

The previous prime is 21661042216573. The next prime is 21661042216661. The reversal of 21661042216643 is 34661224016612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21661042216643 - 2¹⁰ = 21661042215619 is a prime.

It is a super-2 number, since 2×21661042216643² (a number of 27 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21661042216594 and 21661042216603.

It is not a weakly prime, because it can be changed into another prime (21661042216043) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830521108321 + 10830521108322.

It is an arithmetic number, because the mean of its divisors is an integer number (10830521108322).

Almost surely, 2^{21661042216643} is an apocalyptic number.

21661042216643 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661042216643 is an equidigital number, since it uses as much as digits as its factorization.

21661042216643 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 497664, while the sum is 44.

The spelling of 21661042216643 in words is "twenty-one trillion, six hundred sixty-one billion, forty-two million, two hundred sixteen thousand, six hundred forty-three".