21493959656 has 128 divisors (see below), whose sum is σ = 46859420160. Its totient is φ = 9154252800.

The previous prime is 21493959653. The next prime is 21493959689. The reversal of 21493959656 is 65695939412.

It is a junction number, because it is equal to n+sod(n) for n = 21493959595 and 21493959604.

It is not an unprimeable number, because it can be changed into a prime (21493959653) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 49869761 + ... + 49870191.

It is an arithmetic number, because the mean of its divisors is an integer number (366089220).

Almost surely, 2^21493959656 is an apocalyptic number.

21493959656 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21493959656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23429710080).

21493959656 is an abundant number, since it is smaller than the sum of its proper divisors (25365460504).

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

21493959656 is a wasteful number, since it uses less digits than its factorization.

21493959656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 955 (or 951 counting only the distinct ones).

The product of its digits is 15746400, while the sum is 59.

The spelling of 21493959656 in words is "twenty-one billion, four hundred ninety-three million, nine hundred fifty-nine thousand, six hundred fifty-six".