21123187 has 2 divisors, whose sum is σ = 21123188. Its totient is φ = 21123186.

The previous prime is 21123181. The next prime is 21123211. The reversal of 21123187 is 78132112.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21123187 is a prime.

It is not a weakly prime, because it can be changed into another prime (21123181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10561593 + 10561594.

It is an arithmetic number, because the mean of its divisors is an integer number (10561594).

Almost surely, 2^21123187 is an apocalyptic number.

21123187 is the 2654-th hex number.

21123187 is a deficient number, since it is larger than the sum of its proper divisors (1).

21123187 is an equidigital number, since it uses as much as digits as its factorization.

21123187 is an evil number, because the sum of its binary digits is even.

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

The square root of 21123187 is about 4595.9968450816. The cubic root of 21123187 is about 276.4308322378.

Adding to 21123187 its reverse (78132112), we get a palindrome (99255299).

The spelling of 21123187 in words is "twenty-one million, one hundred twenty-three thousand, one hundred eighty-seven".