20909281 has 2 divisors, whose sum is σ = 20909282. Its totient is φ = 20909280.

The previous prime is 20909209. The next prime is 20909297. The reversal of 20909281 is 18290902.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16329681 + 4579600 = 4041^2 + 2140^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20909281 is a prime.

It is a super-2 number, since 2×20909281² = 874396063873922, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (20909081) 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 as a sum of consecutive naturals, namely, 10454640 + 10454641.

It is an arithmetic number, because the mean of its divisors is an integer number (10454641).

Almost surely, 2^20909281 is an apocalyptic number.

It is an amenable number.

20909281 is a deficient number, since it is larger than the sum of its proper divisors (1).

20909281 is an equidigital number, since it uses as much as digits as its factorization.

20909281 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2592, while the sum is 31.

The square root of 20909281 is about 4572.6667274141. Note that the first 3 decimals coincide. The cubic root of 20909281 is about 275.4945634811.

The spelling of 20909281 in words is "twenty million, nine hundred nine thousand, two hundred eighty-one".