21000320161 has 2 divisors, whose sum is σ = 21000320162. Its totient is φ = 21000320160.

The previous prime is 21000320137. The next prime is 21000320183. The reversal of 21000320161 is 16102300012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20712678561 + 287641600 = 143919^2 + 16960^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21000320161 is a prime.

It is not a weakly prime, because it can be changed into another prime (21000320261) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500160080 + 10500160081.

It is an arithmetic number, because the mean of its divisors is an integer number (10500160081).

Almost surely, 2^21000320161 is an apocalyptic number.

It is an amenable number.

21000320161 is a deficient number, since it is larger than the sum of its proper divisors (1).

21000320161 is an equidigital number, since it uses as much as digits as its factorization.

21000320161 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 72, while the sum is 16.

Adding to 21000320161 its reverse (16102300012), we get a palindrome (37102620173).

The spelling of 21000320161 in words is "twenty-one billion, three hundred twenty thousand, one hundred sixty-one".