21006819 has 6 divisors (see below), whose sum is σ = 30343196. Its totient is φ = 14004540.

The previous prime is 21006803. The next prime is 21006829. The reversal of 21006819 is 91860012.

It is not a de Polignac number, because 21006819 - 2⁴ = 21006803 is a prime.

It is a super-2 number, since 2×21006819² = 882572888997522, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21006792 and 21006801.

It is not an unprimeable number, because it can be changed into a prime (21006829) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1167037 + ... + 1167054.

Almost surely, 2^21006819 is an apocalyptic number.

21006819 is a deficient number, since it is larger than the sum of its proper divisors (9336377).

21006819 is a wasteful number, since it uses less digits than its factorization.

21006819 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2334097 (or 2334094 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 27.

The square root of 21006819 is about 4583.3196484644. The cubic root of 21006819 is about 275.9222764763.

The spelling of 21006819 in words is "twenty-one million, six thousand, eight hundred nineteen".