21260781 has 6 divisors (see below), whose sum is σ = 30710030. Its totient is φ = 14173848.

The previous prime is 21260749. The next prime is 21260797. The reversal of 21260781 is 18706212.

It can be written as a sum of positive squares in only one way, i.e., 21206025 + 54756 = 4605^2 + 234^2 .

It is not a de Polignac number, because 21260781 - 2⁵ = 21260749 is a prime.

It is a super-2 number, since 2×21260781² = 904041617459922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21260711) 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, 1181146 + ... + 1181163.

Almost surely, 2^21260781 is an apocalyptic number.

It is an amenable number.

21260781 is a deficient number, since it is larger than the sum of its proper divisors (9449249).

21260781 is a wasteful number, since it uses less digits than its factorization.

21260781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2362315 (or 2362312 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21260781 is about 4610.9414440003. The cubic root of 21260781 is about 277.0297465307.

Adding to 21260781 its reverse (18706212), we get a palindrome (39966993).

The spelling of 21260781 in words is "twenty-one million, two hundred sixty thousand, seven hundred eighty-one".