21778137 has 6 divisors (see below), whose sum is σ = 31457322. Its totient is φ = 14518752.

The previous prime is 21778117. The next prime is 21778157. The reversal of 21778137 is 73187712.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21778117) and next prime (21778157).

It can be written as a sum of positive squares in only one way, i.e., 19501056 + 2277081 = 4416^2 + 1509^2 .

It is not a de Polignac number, because 21778137 - 2¹⁵ = 21745369 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21778117) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1209888 + ... + 1209905.

It is an arithmetic number, because the mean of its divisors is an integer number (5242887).

Almost surely, 2^21778137 is an apocalyptic number.

It is an amenable number.

21778137 is a deficient number, since it is larger than the sum of its proper divisors (9679185).

21778137 is a wasteful number, since it uses less digits than its factorization.

21778137 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2419799 (or 2419796 counting only the distinct ones).

The product of its digits is 16464, while the sum is 36.

The square root of 21778137 is about 4666.7051546032. The cubic root of 21778137 is about 279.2588263731.

The spelling of 21778137 in words is "twenty-one million, seven hundred seventy-eight thousand, one hundred thirty-seven".