21217122215661 has 8 divisors (see below), whose sum is σ = 28292688908064. Its totient is φ = 14143151833520.

The previous prime is 21217122215659. The next prime is 21217122215677. The reversal of 21217122215661 is 16651222171212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21217122215661 - 2¹ = 21217122215659 is a prime.

It is a super-2 number, since 2×21217122215661² (a number of 27 digits) contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21217122215621) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 399046551 + ... + 399099716.

It is an arithmetic number, because the mean of its divisors is an integer number (3536586113508).

Almost surely, 2^{21217122215661} is an apocalyptic number.

It is an amenable number.

21217122215661 is a deficient number, since it is larger than the sum of its proper divisors (7075566692403).

21217122215661 is an equidigital number, since it uses as much as digits as its factorization.

21217122215661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 798155131.

The product of its digits is 40320, while the sum is 39.

Adding to 21217122215661 its reverse (16651222171212), we get a palindrome (37868344386873).

The spelling of 21217122215661 in words is "twenty-one trillion, two hundred seventeen billion, one hundred twenty-two million, two hundred fifteen thousand, six hundred sixty-one".