21151111221 has 48 divisors (see below), whose sum is σ = 33378718464. Its totient is φ = 12854587392.

The previous prime is 21151111211. The next prime is 21151111271. The reversal of 21151111221 is 12211115112.

It is a happy number.

21151111221 is a `hidden beast` number, since 21 + 1 + 511 + 112 + 21 = 666.

It is not a de Polignac number, because 21151111221 - 2¹¹ = 21151109173 is a prime.

It is a super-2 number, since 2×21151111221² (a number of 21 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21151111194 and 21151111203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21151111211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 682366 + ... + 712688.

It is an arithmetic number, because the mean of its divisors is an integer number (695389968).

Almost surely, 2^21151111221 is an apocalyptic number.

It is an amenable number.

21151111221 is a deficient number, since it is larger than the sum of its proper divisors (12227607243).

21151111221 is a wasteful number, since it uses less digits than its factorization.

21151111221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30490 (or 30487 counting only the distinct ones).

The product of its digits is 40, while the sum is 18.

Adding to 21151111221 its reverse (12211115112), we get a palindrome (33362226333).

The spelling of 21151111221 in words is "twenty-one billion, one hundred fifty-one million, one hundred eleven thousand, two hundred twenty-one".