21878149 has 2 divisors, whose sum is σ = 21878150. Its totient is φ = 21878148.

The previous prime is 21878123. The next prime is 21878243. The reversal of 21878149 is 94187812.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17489124 + 4389025 = 4182^2 + 2095^2 .

It is a cyclic number.

It is not a de Polignac number, because 21878149 - 2⁹ = 21877637 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21878449) 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 as a sum of consecutive naturals, namely, 10939074 + 10939075.

It is an arithmetic number, because the mean of its divisors is an integer number (10939075).

Almost surely, 2^21878149 is an apocalyptic number.

It is an amenable number.

21878149 is a deficient number, since it is larger than the sum of its proper divisors (1).

21878149 is an equidigital number, since it uses as much as digits as its factorization.

21878149 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 32256, while the sum is 40.

The square root of 21878149 is about 4677.4083636133. The cubic root of 21878149 is about 279.6856548821.

The spelling of 21878149 in words is "twenty-one million, eight hundred seventy-eight thousand, one hundred forty-nine".