21213187 has 2 divisors, whose sum is σ = 21213188. Its totient is φ = 21213186.

The previous prime is 21213163. The next prime is 21213193. The reversal of 21213187 is 78131212.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21213187 - 2¹¹ = 21211139 is a prime.

It is not a weakly prime, because it can be changed into another prime (21213287) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606593 + 10606594.

It is an arithmetic number, because the mean of its divisors is an integer number (10606594).

Almost surely, 2^21213187 is an apocalyptic number.

21213187 is a deficient number, since it is larger than the sum of its proper divisors (1).

21213187 is an equidigital number, since it uses as much as digits as its factorization.

21213187 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 672, while the sum is 25.

The square root of 21213187 is about 4605.7775673604. Note that the first 3 decimals coincide. The cubic root of 21213187 is about 276.8228741594.

Adding to 21213187 its reverse (78131212), we get a palindrome (99344399).

The spelling of 21213187 in words is "twenty-one million, two hundred thirteen thousand, one hundred eighty-seven".