1687390021 has 2 divisors, whose sum is σ = 1687390022. Its totient is φ = 1687390020.

The previous prime is 1687389989. The next prime is 1687390121. The reversal of 1687390021 is 1200937861.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1280924100 + 406465921 = 35790^2 + 20161^2 .

It is a cyclic number.

It is not a de Polignac number, because 1687390021 - 2⁵ = 1687389989 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1687390121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 843695010 + 843695011.

It is an arithmetic number, because the mean of its divisors is an integer number (843695011).

Almost surely, 2^1687390021 is an apocalyptic number.

It is an amenable number.

1687390021 is a deficient number, since it is larger than the sum of its proper divisors (1).

1687390021 is an equidigital number, since it uses as much as digits as its factorization.

1687390021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 18144, while the sum is 37.

The square root of 1687390021 is about 41077.8531693174. The cubic root of 1687390021 is about 1190.5249245950.

The spelling of 1687390021 in words is "one billion, six hundred eighty-seven million, three hundred ninety thousand, twenty-one".