21181899 has 12 divisors (see below), whose sum is σ = 28721768. Its totient is φ = 13883040.

The previous prime is 21181891. The next prime is 21181907. The reversal of 21181899 is 99818112.

21181899 = T₇₂₅ + T₇₂₆ + ... + T₇₉₇.

It is an interprime number because it is at equal distance from previous prime (21181891) and next prime (21181907).

It is not a de Polignac number, because 21181899 - 2³ = 21181891 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21181891) 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 in 11 ways as a sum of consecutive naturals, for example, 67954 + ... + 68264.

Almost surely, 2^21181899 is an apocalyptic number.

21181899 is a deficient number, since it is larger than the sum of its proper divisors (7539869).

21181899 is an frugal number, since it uses more digits than its factorization.

21181899 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 698 (or 387 counting only the distinct ones).

The product of its digits is 10368, while the sum is 39.

The square root of 21181899 is about 4602.3797105411. The cubic root of 21181899 is about 276.6867089237.

The spelling of 21181899 in words is "twenty-one million, one hundred eighty-one thousand, eight hundred ninety-nine".