21303781 has 2 divisors, whose sum is σ = 21303782. Its totient is φ = 21303780.

The previous prime is 21303757. The next prime is 21303787. The reversal of 21303781 is 18730312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13653025 + 7650756 = 3695^2 + 2766^2 .

It is a cyclic number.

It is not a de Polignac number, because 21303781 - 2¹¹ = 21301733 is a prime.

It is a super-2 number, since 2×21303781² = 907702169791922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21303787) 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 as a sum of consecutive naturals, namely, 10651890 + 10651891.

It is an arithmetic number, because the mean of its divisors is an integer number (10651891).

Almost surely, 2^21303781 is an apocalyptic number.

It is an amenable number.

21303781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21303781 is an equidigital number, since it uses as much as digits as its factorization.

21303781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1008, while the sum is 25.

The square root of 21303781 is about 4615.6019109104. The cubic root of 21303781 is about 277.2163852880.

The spelling of 21303781 in words is "twenty-one million, three hundred three thousand, seven hundred eighty-one".