21367781 has 2 divisors, whose sum is σ = 21367782. Its totient is φ = 21367780.

The previous prime is 21367777. The next prime is 21367807. The reversal of 21367781 is 18776312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17926756 + 3441025 = 4234^2 + 1855^2 .

It is a cyclic number.

It is not a de Polignac number, because 21367781 - 2² = 21367777 is a prime.

It is a super-2 number, since 2×21367781² = 913164129727922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21367721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10683890 + 10683891.

It is an arithmetic number, because the mean of its divisors is an integer number (10683891).

Almost surely, 2^21367781 is an apocalyptic number.

It is an amenable number.

21367781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21367781 is an equidigital number, since it uses as much as digits as its factorization.

21367781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14112, while the sum is 35.

The square root of 21367781 is about 4622.5297186714. The cubic root of 21367781 is about 277.4937087013.

The spelling of 21367781 in words is "twenty-one million, three hundred sixty-seven thousand, seven hundred eighty-one".