21012121 has 8 divisors (see below), whose sum is σ = 23000264. Its totient is φ = 19077120.

The previous prime is 21012091. The next prime is 21012127. The reversal of 21012121 is 12121012.

21012121 is an esthetic number in base 10, because in such base its adjacent digits differ by 1.

It can be written as a sum of positive squares in 4 ways, for example, as 409600 + 20602521 = 640^2 + 4539^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21012121 - 2¹³ = 21003929 is a prime.

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

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21012098 and 21012107.

It is not an unprimeable number, because it can be changed into a prime (21012127) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12456 + ... + 14041.

It is an arithmetic number, because the mean of its divisors is an integer number (2875033).

Almost surely, 2^21012121 is an apocalyptic number.

It is an amenable number.

21012121 is a deficient number, since it is larger than the sum of its proper divisors (1988143).

21012121 is a wasteful number, since it uses less digits than its factorization.

21012121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26571.

The product of its (nonzero) digits is 8, while the sum is 10.

The square root of 21012121 is about 4583.8980136997. The cubic root of 21012121 is about 275.9454882541.

Adding to 21012121 its reverse (12121012), we get a palindrome (33133133).

It can be divided in two parts, 21012 and 121, that multiplied together give a palindrome (2542452).

The spelling of 21012121 in words is "twenty-one million, twelve thousand, one hundred twenty-one".