21165121 has 2 divisors, whose sum is σ = 21165122. Its totient is φ = 21165120.

The previous prime is 21165097. The next prime is 21165149. The reversal of 21165121 is 12156112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15689521 + 5475600 = 3961^2 + 2340^2 .

It is a cyclic number.

It is not a de Polignac number, because 21165121 - 2¹³ = 21156929 is a prime.

It is not a weakly prime, because it can be changed into another prime (21165421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10582560 + 10582561.

It is an arithmetic number, because the mean of its divisors is an integer number (10582561).

Almost surely, 2^21165121 is an apocalyptic number.

It is an amenable number.

21165121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21165121 is an equidigital number, since it uses as much as digits as its factorization.

21165121 is an evil number, because the sum of its binary digits is even.

The product of its digits is 120, while the sum is 19.

The square root of 21165121 is about 4600.5565967609. The cubic root of 21165121 is about 276.6136359061.

Subtracting from 21165121 its reverse (12156112), we obtain a palindrome (9009009).

It can be divided in two parts, 211651 and 21, that multiplied together give a triangular number (4444671 = T₂₉₈₁).

The spelling of 21165121 in words is "twenty-one million, one hundred sixty-five thousand, one hundred twenty-one".