21216405023646 has 16 divisors (see below), whose sum is σ = 48494640054144. Its totient is φ = 6061830006744.

The previous prime is 21216405023633. The next prime is 21216405023647. The reversal of 21216405023646 is 64632050461212.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (42), and also a Moran number because the ratio is a prime number: 505152500563 = 21216405023646 / (2 + 1 + 2 + 1 + 6 + 4 + 0 + 5 + 0 + 2 + 3 + 6 + 4 + 6).

It is a junction number, because it is equal to n+sod(n) for n = 21216405023598 and 21216405023607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216405023647) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 252576250240 + ... + 252576250323.

It is an arithmetic number, because the mean of its divisors is an integer number (3030915003384).

Almost surely, 2^{21216405023646} is an apocalyptic number.

21216405023646 is an abundant number, since it is smaller than the sum of its proper divisors (27278235030498).

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

21216405023646 is a wasteful number, since it uses less digits than its factorization.

21216405023646 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 505152500575.

The product of its (nonzero) digits is 414720, while the sum is 42.

Adding to 21216405023646 its reverse (64632050461212), we get a palindrome (85848455484858).

The spelling of 21216405023646 in words is "twenty-one trillion, two hundred sixteen billion, four hundred five million, twenty-three thousand, six hundred forty-six".