21405216191951 has 4 divisors (see below), whose sum is σ = 21405287918304. Its totient is φ = 21405144465600.

The previous prime is 21405216191911. The next prime is 21405216191999. The reversal of 21405216191951 is 15919161250412.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21405216191951 - 2¹⁰ = 21405216190927 is a prime.

It is a super-2 number, since 2×21405216191951² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21405216191896 and 21405216191905.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21405216191911) 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, 35413655 + ... + 36013016.

It is an arithmetic number, because the mean of its divisors is an integer number (5351321979576).

Almost surely, 2^{21405216191951} is an apocalyptic number.

21405216191951 is a deficient number, since it is larger than the sum of its proper divisors (71726353).

21405216191951 is an equidigital number, since it uses as much as digits as its factorization.

21405216191951 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 71726352.

The product of its (nonzero) digits is 194400, while the sum is 47.

The spelling of 21405216191951 in words is "twenty-one trillion, four hundred five billion, two hundred sixteen million, one hundred ninety-one thousand, nine hundred fifty-one".