21058781 has 2 divisors, whose sum is σ = 21058782. Its totient is φ = 21058780.

The previous prime is 21058757. The next prime is 21058787. The reversal of 21058781 is 18785012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18705625 + 2353156 = 4325^2 + 1534^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21058781 is a prime.

It is a super-2 number, since 2×21058781² = 886944514411922, which contains 22 as substring.

It is a Chen 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 (21058787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10529390 + 10529391.

It is an arithmetic number, because the mean of its divisors is an integer number (10529391).

Almost surely, 2^21058781 is an apocalyptic number.

It is an amenable number.

21058781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21058781 is an equidigital number, since it uses as much as digits as its factorization.

21058781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4480, while the sum is 32.

The square root of 21058781 is about 4588.9847461067. The cubic root of 21058781 is about 276.1495942174.

The spelling of 21058781 in words is "twenty-one million, fifty-eight thousand, seven hundred eighty-one".