21156643200 has 384 divisors, whose sum is σ = 86882653440. Its totient is φ = 4396032000.

The previous prime is 21156643199. The next prime is 21156643201. The reversal of 21156643200 is 234665112.

It is an interprime number because it is at equal distance from previous prime (21156643199) and next prime (21156643201).

It is a tau number, because it is divible by the number of its divisors (384).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21156643201) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 724890 + ... + 753510.

It is an arithmetic number, because the mean of its divisors is an integer number (226256910).

Almost surely, 2^21156643200 is an apocalyptic number.

21156643200 is a gapful number since it is divisible by the number (20) 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 21156643200, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (43441326720).

21156643200 is an abundant number, since it is smaller than the sum of its proper divisors (65726010240).

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

21156643200 is a wasteful number, since it uses less digits than its factorization.

21156643200 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28666 (or 28649 counting only the distinct ones).

The product of its (nonzero) digits is 8640, while the sum is 30.

The spelling of 21156643200 in words is "twenty-one billion, one hundred fifty-six million, six hundred forty-three thousand, two hundred".