21781377 has 12 divisors (see below), whose sum is σ = 31502484. Its totient is φ = 14502240.

The previous prime is 21781367. The next prime is 21781379. The reversal of 21781377 is 77318712.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 17943696 + 3837681 = 4236^2 + 1959^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21781377 is a prime.

It is a super-2 number, since 2×21781377² = 948856768032258, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21781379) by changing a digit.

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 11 ways as a sum of consecutive naturals, for example, 12627 + ... + 14247.

It is an arithmetic number, because the mean of its divisors is an integer number (2625207).

Almost surely, 2^21781377 is an apocalyptic number.

It is an amenable number.

21781377 is a deficient number, since it is larger than the sum of its proper divisors (9721107).

21781377 is a wasteful number, since it uses less digits than its factorization.

21781377 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3120 (or 3117 counting only the distinct ones).

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

The square root of 21781377 is about 4667.0522816870. The cubic root of 21781377 is about 279.2726744160.

The spelling of 21781377 in words is "twenty-one million, seven hundred eighty-one thousand, three hundred seventy-seven".