21781005 has 16 divisors (see below), whose sum is σ = 35661120. Its totient is φ = 11346048.

The previous prime is 21780991. The next prime is 21781021. The reversal of 21781005 is 50018712.

It is not a de Polignac number, because 21781005 - 2⁴ = 21780989 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 16240 + ... + 17529.

It is an arithmetic number, because the mean of its divisors is an integer number (2228820).

Almost surely, 2^21781005 is an apocalyptic number.

It is an amenable number.

21781005 is a deficient number, since it is larger than the sum of its proper divisors (13880115).

21781005 is a wasteful number, since it uses less digits than its factorization.

21781005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33820.

The product of its (nonzero) digits is 560, while the sum is 24.

The square root of 21781005 is about 4667.0124276672. The cubic root of 21781005 is about 279.2710845253.

Adding to 21781005 its reverse (50018712), we get a palindrome (71799717).

The spelling of 21781005 in words is "twenty-one million, seven hundred eighty-one thousand, five".