21312787 has 2 divisors, whose sum is σ = 21312788. Its totient is φ = 21312786.

The previous prime is 21312763. The next prime is 21312793. The reversal of 21312787 is 78721312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21312787 - 2¹¹ = 21310739 is a prime.

It is not a weakly prime, because it can be changed into another prime (21312727) 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 as a sum of consecutive naturals, namely, 10656393 + 10656394.

It is an arithmetic number, because the mean of its divisors is an integer number (10656394).

Almost surely, 2^21312787 is an apocalyptic number.

21312787 is a deficient number, since it is larger than the sum of its proper divisors (1).

21312787 is an equidigital number, since it uses as much as digits as its factorization.

21312787 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4704, while the sum is 31.

The square root of 21312787 is about 4616.5774118929. The cubic root of 21312787 is about 277.2554434415.

The spelling of 21312787 in words is "twenty-one million, three hundred twelve thousand, seven hundred eighty-seven".