21661431533213 has 4 divisors (see below), whose sum is σ = 21663212473728. Its totient is φ = 21659650592700.

The previous prime is 21661431533197. The next prime is 21661431533243. The reversal of 21661431533213 is 31233513416612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21661431533213 - 2⁴ = 21661431533197 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661431533243) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 890452013 + ... + 890476338.

It is an arithmetic number, because the mean of its divisors is an integer number (5415803118432).

Almost surely, 2^{21661431533213} is an apocalyptic number.

It is an amenable number.

21661431533213 is a deficient number, since it is larger than the sum of its proper divisors (1780940515).

21661431533213 is a wasteful number, since it uses less digits than its factorization.

21661431533213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1780940514.

The product of its digits is 233280, while the sum is 41.

Adding to 21661431533213 its reverse (31233513416612), we get a palindrome (52894944949825).

The spelling of 21661431533213 in words is "twenty-one trillion, six hundred sixty-one billion, four hundred thirty-one million, five hundred thirty-three thousand, two hundred thirteen".