21500161 has 2 divisors, whose sum is σ = 21500162. Its totient is φ = 21500160.

The previous prime is 21500137. The next prime is 21500177. The reversal of 21500161 is 16100512.

It is a happy number.

It is an a-pointer prime, because the next prime (21500177) can be obtained adding 21500161 to its sum of digits (16).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18147600 + 3352561 = 4260^2 + 1831^2 .

It is a cyclic number.

It is not a de Polignac number, because 21500161 - 2⁹ = 21499649 is a prime.

It is not a weakly prime, because it can be changed into another prime (21500111) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10750080 + 10750081.

It is an arithmetic number, because the mean of its divisors is an integer number (10750081).

Almost surely, 2^21500161 is an apocalyptic number.

It is an amenable number.

21500161 is a deficient number, since it is larger than the sum of its proper divisors (1).

21500161 is an equidigital number, since it uses as much as digits as its factorization.

21500161 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 60, while the sum is 16.

The square root of 21500161 is about 4636.8266087918. The cubic root of 21500161 is about 278.0655824088.

Adding to 21500161 its reverse (16100512), we get a palindrome (37600673).

The spelling of 21500161 in words is "twenty-one million, five hundred thousand, one hundred sixty-one".