21661042216555 has 32 divisors (see below), whose sum is σ = 31592581756416. Its totient is φ = 13917979313664.

The previous prime is 21661042216553. The next prime is 21661042216571. The reversal of 21661042216555 is 55561224016612.

It is a cyclic number.

It is not a de Polignac number, because 21661042216555 - 2¹ = 21661042216553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21661042216553) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 80052409 + ... + 80322538.

It is an arithmetic number, because the mean of its divisors is an integer number (987268179888).

Almost surely, 2^{21661042216555} is an apocalyptic number.

21661042216555 is a deficient number, since it is larger than the sum of its proper divisors (9931539539861).

21661042216555 is a wasteful number, since it uses less digits than its factorization.

21661042216555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 160375203.

The product of its (nonzero) digits is 864000, while the sum is 46.

The spelling of 21661042216555 in words is "twenty-one trillion, six hundred sixty-one billion, forty-two million, two hundred sixteen thousand, five hundred fifty-five".