21758121 has 24 divisors (see below), whose sum is σ = 39184704. Its totient is φ = 11302560.

The previous prime is 21758119. The next prime is 21758123. The reversal of 21758121 is 12185712.

It is an interprime number because it is at equal distance from previous prime (21758119) and next prime (21758123).

It is not a de Polignac number, because 21758121 - 2¹ = 21758119 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21758123) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 15006 + ... + 16391.

It is an arithmetic number, because the mean of its divisors is an integer number (1632696).

Almost surely, 2^21758121 is an apocalyptic number.

21758121 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21758121 is a deficient number, since it is larger than the sum of its proper divisors (17426583).

21758121 is a wasteful number, since it uses less digits than its factorization.

21758121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31421 (or 31418 counting only the distinct ones).

The product of its digits is 1120, while the sum is 27.

The square root of 21758121 is about 4664.5601078773. The cubic root of 21758121 is about 279.1732457745.

It can be divided in two parts, 2175 and 8121, that added together give a triangular number (10296 = T₁₄₃).

The spelling of 21758121 in words is "twenty-one million, seven hundred fifty-eight thousand, one hundred twenty-one".