21786481 has 2 divisors, whose sum is σ = 21786482. Its totient is φ = 21786480.

The previous prime is 21786467. The next prime is 21786487. The reversal of 21786481 is 18468712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13024881 + 8761600 = 3609^2 + 2960^2 .

It is a cyclic number.

It is not a de Polignac number, because 21786481 - 2⁵ = 21786449 is a prime.

It is a super-2 number, since 2×21786481² = 949301508726722, which contains 22 as substring.

It is equal to p_1376578 and since 21786481 and 1376578 have the same sum of digits, it is a Honaker prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21786481.

It is not a weakly prime, because it can be changed into another prime (21786487) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10893240 + 10893241.

It is an arithmetic number, because the mean of its divisors is an integer number (10893241).

Almost surely, 2^21786481 is an apocalyptic number.

It is an amenable number.

21786481 is a deficient number, since it is larger than the sum of its proper divisors (1).

21786481 is an equidigital number, since it uses as much as digits as its factorization.

21786481 is an evil number, because the sum of its binary digits is even.

The product of its digits is 21504, while the sum is 37.

The square root of 21786481 is about 4667.5990616162. The cubic root of 21786481 is about 279.2944865725.

The spelling of 21786481 in words is "twenty-one million, seven hundred eighty-six thousand, four hundred eighty-one".