21012161 has 2 divisors, whose sum is σ = 21012162. Its totient is φ = 21012160.

The previous prime is 21012151. The next prime is 21012181. The reversal of 21012161 is 16121012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20757136 + 255025 = 4556^2 + 505^2 .

It is a cyclic number.

It is not a de Polignac number, because 21012161 - 2¹⁸ = 20750017 is a prime.

It is a Chen prime.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (21012151) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10506080 + 10506081.

It is an arithmetic number, because the mean of its divisors is an integer number (10506081).

Almost surely, 2^21012161 is an apocalyptic number.

It is an amenable number.

21012161 is a deficient number, since it is larger than the sum of its proper divisors (1).

21012161 is an equidigital number, since it uses as much as digits as its factorization.

21012161 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 24, while the sum is 14.

The square root of 21012161 is about 4583.9023767964. The cubic root of 21012161 is about 275.9456633564.

Adding to 21012161 its reverse (16121012), we get a palindrome (37133173).

The spelling of 21012161 in words is "twenty-one million, twelve thousand, one hundred sixty-one".