1664686421 has 2 divisors, whose sum is σ = 1664686422. Its totient is φ = 1664686420.

The previous prime is 1664686369. The next prime is 1664686447. The reversal of 1664686421 is 1246864661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1533583921 + 131102500 = 39161^2 + 11450^2 .

It is a cyclic number.

It is not a de Polignac number, because 1664686421 - 2¹⁰ = 1664685397 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1664686451) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 832343210 + 832343211.

It is an arithmetic number, because the mean of its divisors is an integer number (832343211).

Almost surely, 2^1664686421 is an apocalyptic number.

It is an amenable number.

1664686421 is a deficient number, since it is larger than the sum of its proper divisors (1).

1664686421 is an equidigital number, since it uses as much as digits as its factorization.

1664686421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 331776, while the sum is 44.

The square root of 1664686421 is about 40800.5688808379. The cubic root of 1664686421 is about 1185.1613472316.

The spelling of 1664686421 in words is "one billion, six hundred sixty-four million, six hundred eighty-six thousand, four hundred twenty-one".