21402121 has 16 divisors (see below), whose sum is σ = 24837120. Its totient is φ = 18279360.

The previous prime is 21402119. The next prime is 21402137. The reversal of 21402121 is 12120412.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 21402121 - 2¹ = 21402119 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (13).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21402181) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8115 + ... + 10423.

It is an arithmetic number, because the mean of its divisors is an integer number (1552320).

Almost surely, 2^21402121 is an apocalyptic number.

It is an amenable number.

21402121 is a deficient number, since it is larger than the sum of its proper divisors (3434999).

21402121 is a wasteful number, since it uses less digits than its factorization.

21402121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2376.

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 21402121 is about 4626.2426438742. The cubic root of 21402121 is about 277.6422818230.

Adding to 21402121 its product of nonzero digits (32), we get a triangular number (21402153 = T₆₅₄₂).

Adding to 21402121 its reverse (12120412), we get a palindrome (33522533).

The spelling of 21402121 in words is "twenty-one million, four hundred two thousand, one hundred twenty-one".