1688629721 has 2 divisors, whose sum is σ = 1688629722. Its totient is φ = 1688629720.

The previous prime is 1688629699. The next prime is 1688629727. The reversal of 1688629721 is 1279268861.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 894010000 + 794619721 = 29900^2 + 28189^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1688629721 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1688629721.

It is not a weakly prime, because it can be changed into another prime (1688629727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 844314860 + 844314861.

It is an arithmetic number, because the mean of its divisors is an integer number (844314861).

Almost surely, 2^1688629721 is an apocalyptic number.

It is an amenable number.

1688629721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1688629721 is an equidigital number, since it uses as much as digits as its factorization.

1688629721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 580608, while the sum is 50.

The square root of 1688629721 is about 41092.9400384056. The cubic root of 1688629721 is about 1190.8164067931.

The spelling of 1688629721 in words is "one billion, six hundred eighty-eight million, six hundred twenty-nine thousand, seven hundred twenty-one".