21801972217 has 2 divisors, whose sum is σ = 21801972218. Its totient is φ = 21801972216.

The previous prime is 21801972163. The next prime is 21801972221. The reversal of 21801972217 is 71227910812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17469173241 + 4332798976 = 132171^2 + 65824^2 .

It is a cyclic number.

It is not a de Polignac number, because 21801972217 - 2¹⁵ = 21801939449 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21801972217.

It is not a weakly prime, because it can be changed into another prime (21801972277) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10900986108 + 10900986109.

It is an arithmetic number, because the mean of its divisors is an integer number (10900986109).

Almost surely, 2^21801972217 is an apocalyptic number.

It is an amenable number.

21801972217 is a deficient number, since it is larger than the sum of its proper divisors (1).

21801972217 is an equidigital number, since it uses as much as digits as its factorization.

21801972217 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 28224, while the sum is 40.

The spelling of 21801972217 in words is "twenty-one billion, eight hundred one million, nine hundred seventy-two thousand, two hundred seventeen".