21620734205209 has 2 divisors, whose sum is σ = 21620734205210. Its totient is φ = 21620734205208.

The previous prime is 21620734205117. The next prime is 21620734205281. The reversal of 21620734205209 is 90250243702612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21504810979584 + 115923225625 = 4637328^2 + 340475^2 .

It is a cyclic number.

It is not a de Polignac number, because 21620734205209 - 2⁹ = 21620734204697 is a prime.

It is a super-2 number, since 2×21620734205209² (a number of 27 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21620734205299) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10810367102604 + 10810367102605.

It is an arithmetic number, because the mean of its divisors is an integer number (10810367102605).

Almost surely, 2^{21620734205209} is an apocalyptic number.

It is an amenable number.

21620734205209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21620734205209 is an equidigital number, since it uses as much as digits as its factorization.

21620734205209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 362880, while the sum is 43.

The spelling of 21620734205209 in words is "twenty-one trillion, six hundred twenty billion, seven hundred thirty-four million, two hundred five thousand, two hundred nine".