21399671808 has 264 divisors, whose sum is σ = 65969520552. Its totient is φ = 6657933312.

The previous prime is 21399671807. The next prime is 21399671809. The reversal of 21399671808 is 80817699312.

It is an interprime number because it is at equal distance from previous prime (21399671807) and next prime (21399671809).

It can be written as a sum of positive squares in 4 ways, for example, as 10709766144 + 10689905664 = 103488^2 + 103392^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21399671801) 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 23 ways as a sum of consecutive naturals, for example, 21463566 + ... + 21464562.

Almost surely, 2^21399671808 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21399671808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32984760276).

21399671808 is an abundant number, since it is smaller than the sum of its proper divisors (44569848744).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21399671808 is a wasteful number, since it uses less digits than its factorization.

21399671808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1177 (or 1156 counting only the distinct ones).

The product of its (nonzero) digits is 1306368, while the sum is 54.

The spelling of 21399671808 in words is "twenty-one billion, three hundred ninety-nine million, six hundred seventy-one thousand, eight hundred eight".