21787819 has 2 divisors, whose sum is σ = 21787820. Its totient is φ = 21787818.

The previous prime is 21787817. The next prime is 21787853. The reversal of 21787819 is 91878712.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21787819 - 2¹ = 21787817 is a prime.

It is a super-2 number, since 2×21787819² = 949418113553522, which contains 22 as substring.

Together with 21787817, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21787811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10893909 + 10893910.

It is an arithmetic number, because the mean of its divisors is an integer number (10893910).

Almost surely, 2^21787819 is an apocalyptic number.

21787819 is a deficient number, since it is larger than the sum of its proper divisors (1).

21787819 is an equidigital number, since it uses as much as digits as its factorization.

21787819 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 56448, while the sum is 43.

The square root of 21787819 is about 4667.7423879216. The cubic root of 21787819 is about 279.3002040076.

The spelling of 21787819 in words is "twenty-one million, seven hundred eighty-seven thousand, eight hundred nineteen".