20651681 has 2 divisors, whose sum is σ = 20651682. Its totient is φ = 20651680.

The previous prime is 20651641. The next prime is 20651693. The reversal of 20651681 is 18615602.

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., 16072081 + 4579600 = 4009^2 + 2140^2 .

It is a cyclic number.

It is not a de Polignac number, because 20651681 - 2¹⁰ = 20650657 is a prime.

It is a super-2 number, since 2×20651681² = 852983856251522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (20651641) 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, 10325840 + 10325841.

It is an arithmetic number, because the mean of its divisors is an integer number (10325841).

Almost surely, 2^20651681 is an apocalyptic number.

It is an amenable number.

20651681 is a deficient number, since it is larger than the sum of its proper divisors (1).

20651681 is an equidigital number, since it uses as much as digits as its factorization.

20651681 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2880, while the sum is 29.

The square root of 20651681 is about 4544.4120631827. The cubic root of 20651681 is about 274.3585313112.

The spelling of 20651681 in words is "twenty million, six hundred fifty-one thousand, six hundred eighty-one".