21690121 has 2 divisors, whose sum is σ = 21690122. Its totient is φ = 21690120.

The previous prime is 21690089. The next prime is 21690131. The reversal of 21690121 is 12109612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16491721 + 5198400 = 4061^2 + 2280^2 .

It is a cyclic number.

It is not a de Polignac number, because 21690121 - 2⁵ = 21690089 is a prime.

It is a super-2 number, since 2×21690121² = 940922697989282, which contains 22 as substring.

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

It is a junction number, because it is equal to n+sod(n) for n = 21690092 and 21690101.

It is not a weakly prime, because it can be changed into another prime (21690131) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10845060 + 10845061.

It is an arithmetic number, because the mean of its divisors is an integer number (10845061).

Almost surely, 2^21690121 is an apocalyptic number.

It is an amenable number.

21690121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21690121 is an equidigital number, since it uses as much as digits as its factorization.

21690121 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 216, while the sum is 22.

The square root of 21690121 is about 4657.2653993519. The cubic root of 21690121 is about 278.8821116948.

Adding to 21690121 its reverse (12109612), we get a palindrome (33799733).

The spelling of 21690121 in words is "twenty-one million, six hundred ninety thousand, one hundred twenty-one".