21247819 has 2 divisors, whose sum is σ = 21247820. Its totient is φ = 21247818.

The previous prime is 21247789. The next prime is 21247823. The reversal of 21247819 is 91874212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21247819 - 2¹¹ = 21245771 is a prime.

It is a super-2 number, since 2×21247819² = 902939624513522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21247019) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10623909 + 10623910.

It is an arithmetic number, because the mean of its divisors is an integer number (10623910).

Almost surely, 2^21247819 is an apocalyptic number.

21247819 is a deficient number, since it is larger than the sum of its proper divisors (1).

21247819 is an equidigital number, since it uses as much as digits as its factorization.

21247819 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8064, while the sum is 34.

The square root of 21247819 is about 4609.5356599120. The cubic root of 21247819 is about 276.9734364393.

The spelling of 21247819 in words is "twenty-one million, two hundred forty-seven thousand, eight hundred nineteen".