21566837 has 2 divisors, whose sum is σ = 21566838. Its totient is φ = 21566836.

The previous prime is 21566827. The next prime is 21566873. The reversal of 21566837 is 73866512.

Together with next prime (21566873) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12117361 + 9449476 = 3481^2 + 3074^2 .

It is a cyclic number.

It is not a de Polignac number, because 21566837 - 2⁴ = 21566821 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21566837.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21566827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10783418 + 10783419.

It is an arithmetic number, because the mean of its divisors is an integer number (10783419).

Almost surely, 2^21566837 is an apocalyptic number.

It is an amenable number.

21566837 is a deficient number, since it is larger than the sum of its proper divisors (1).

21566837 is an equidigital number, since it uses as much as digits as its factorization.

21566837 is an evil number, because the sum of its binary digits is even.

The product of its digits is 60480, while the sum is 38.

The square root of 21566837 is about 4644.0108742336. The cubic root of 21566837 is about 278.3527301513.

The spelling of 21566837 in words is "twenty-one million, five hundred sixty-six thousand, eight hundred thirty-seven".