21769681 has 2 divisors, whose sum is σ = 21769682. Its totient is φ = 21769680.

The previous prime is 21769669. The next prime is 21769717. The reversal of 21769681 is 18696712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20930625 + 839056 = 4575^2 + 916^2 .

It is a cyclic number.

It is not a de Polignac number, because 21769681 - 2¹⁷ = 21638609 is a prime.

It is a super-2 number, since 2×21769681² = 947838021683522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21769651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10884840 + 10884841.

It is an arithmetic number, because the mean of its divisors is an integer number (10884841).

Almost surely, 2^21769681 is an apocalyptic number.

It is an amenable number.

21769681 is a deficient number, since it is larger than the sum of its proper divisors (1).

21769681 is an equidigital number, since it uses as much as digits as its factorization.

21769681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 36288, while the sum is 40.

The square root of 21769681 is about 4665.7990741137. The cubic root of 21769681 is about 279.2226782194. Note that the first 3 decimals are identical.

The spelling of 21769681 in words is "twenty-one million, seven hundred sixty-nine thousand, six hundred eighty-one".