21004042251816 has 128 divisors (see below), whose sum is σ = 62894639808000. Its totient is φ = 6456401512704.

The previous prime is 21004042251811. The next prime is 21004042251817. The reversal of 21004042251816 is 61815224040012.

21004042251816 is a `hidden beast` number, since 2 + 1 + 0 + 0 + 404 + 225 + 18 + 16 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (21004042251811) 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, 847536 + ... + 6536543.

It is an arithmetic number, because the mean of its divisors is an integer number (491364373500).

Almost surely, 2^{21004042251816} is an apocalyptic number.

21004042251816 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 21004042251816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31447319904000).

21004042251816 is an abundant number, since it is smaller than the sum of its proper divisors (41890597556184).

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

21004042251816 is a wasteful number, since it uses less digits than its factorization.

21004042251816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7385120 (or 7385110 counting only the distinct ones).

The product of its (nonzero) digits is 30720, while the sum is 36.

Adding to 21004042251816 its reverse (61815224040012), we get a palindrome (82819266291828).

The spelling of 21004042251816 in words is "twenty-one trillion, four billion, forty-two million, two hundred fifty-one thousand, eight hundred sixteen".