21316639 has 2 divisors, whose sum is σ = 21316640. Its totient is φ = 21316638.

The previous prime is 21316619. The next prime is 21316643. The reversal of 21316639 is 93661312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21316639 - 2²³ = 12928031 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21316639.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21316609) 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, 10658319 + 10658320.

It is an arithmetic number, because the mean of its divisors is an integer number (10658320).

Almost surely, 2^21316639 is an apocalyptic number.

21316639 is a deficient number, since it is larger than the sum of its proper divisors (1).

21316639 is an equidigital number, since it uses as much as digits as its factorization.

21316639 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5832, while the sum is 31.

The square root of 21316639 is about 4616.9945852253. The cubic root of 21316639 is about 277.2721458345.

The spelling of 21316639 in words is "twenty-one million, three hundred sixteen thousand, six hundred thirty-nine".