21855437 has 2 divisors, whose sum is σ = 21855438. Its totient is φ = 21855436.

The previous prime is 21855409. The next prime is 21855439. The reversal of 21855437 is 73455812.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13205956 + 8649481 = 3634^2 + 2941^2 .

It is a cyclic number.

It is not a de Polignac number, because 21855437 - 2¹⁴ = 21839053 is a prime.

Together with 21855439, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21855397 and 21855406.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21855439) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10927718 + 10927719.

It is an arithmetic number, because the mean of its divisors is an integer number (10927719).

Almost surely, 2^21855437 is an apocalyptic number.

It is an amenable number.

21855437 is a deficient number, since it is larger than the sum of its proper divisors (1).

21855437 is an equidigital number, since it uses as much as digits as its factorization.

21855437 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 33600, while the sum is 35.

The square root of 21855437 is about 4674.9798930049. The cubic root of 21855437 is about 279.5888395624.

It can be divided in two parts, 21855 and 437, that multiplied together give a triangular number (9550635 = T₄₃₇₀).

The spelling of 21855437 in words is "twenty-one million, eight hundred fifty-five thousand, four hundred thirty-seven".