21655231 has 16 divisors (see below), whose sum is σ = 24905440. Its totient is φ = 18662400.

The previous prime is 21655223. The next prime is 21655247. The reversal of 21655231 is 13255612.

It is a 10-Lehmer number, since φ(21655231) divides (21655231-1)¹⁰.

It is a cyclic number.

It is not a de Polignac number, because 21655231 - 2³ = 21655223 is a prime.

It is a super-2 number, since 2×21655231² = 937898059326722, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21655196 and 21655205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21655201) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17431 + ... + 18631.

It is an arithmetic number, because the mean of its divisors is an integer number (1556590).

Almost surely, 2^21655231 is an apocalyptic number.

21655231 is a deficient number, since it is larger than the sum of its proper divisors (3250209).

21655231 is a wasteful number, since it uses less digits than its factorization.

21655231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1306.

The product of its digits is 1800, while the sum is 25.

The square root of 21655231 is about 4653.5181314786. The cubic root of 21655231 is about 278.7324979795.

It can be divided in two parts, 2165 and 5231, that added together give a square (7396 = 86²).

The spelling of 21655231 in words is "twenty-one million, six hundred fifty-five thousand, two hundred thirty-one".