20689661 has 2 divisors, whose sum is σ = 20689662. Its totient is φ = 20689660.

The previous prime is 20689657. The next prime is 20689699. The reversal of 20689661 is 16698602.

It is an a-pointer prime, because the next prime (20689699) can be obtained adding 20689661 to its sum of digits (38).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18757561 + 1932100 = 4331^2 + 1390^2 .

It is a cyclic number.

It is not a de Polignac number, because 20689661 - 2² = 20689657 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20689621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10344830 + 10344831.

It is an arithmetic number, because the mean of its divisors is an integer number (10344831).

Almost surely, 2^20689661 is an apocalyptic number.

It is an amenable number.

20689661 is a deficient number, since it is larger than the sum of its proper divisors (1).

20689661 is an equidigital number, since it uses as much as digits as its factorization.

20689661 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 31104, while the sum is 38.

The square root of 20689661 is about 4548.5889020662. The cubic root of 20689661 is about 274.5266169945.

The spelling of 20689661 in words is "twenty million, six hundred eighty-nine thousand, six hundred sixty-one".