20701689721 has 2 divisors, whose sum is σ = 20701689722. Its totient is φ = 20701689720.

The previous prime is 20701689719. The next prime is 20701689797. The reversal of 20701689721 is 12798610702.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20299125625 + 402564096 = 142475^2 + 20064^2 .

It is a cyclic number.

It is not a de Polignac number, because 20701689721 - 2¹ = 20701689719 is a prime.

Together with 20701689719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (20701684721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10350844860 + 10350844861.

It is an arithmetic number, because the mean of its divisors is an integer number (10350844861).

Almost surely, 2^20701689721 is an apocalyptic number.

It is an amenable number.

20701689721 is a deficient number, since it is larger than the sum of its proper divisors (1).

20701689721 is an equidigital number, since it uses as much as digits as its factorization.

20701689721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 84672, while the sum is 43.

The spelling of 20701689721 in words is "twenty billion, seven hundred one million, six hundred eighty-nine thousand, seven hundred twenty-one".