999979621 has 2 divisors, whose sum is σ = 999979622. Its totient is φ = 999979620.

The previous prime is 999979619. The next prime is 999979637. The reversal of 999979621 is 126979999.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 795804100 + 204175521 = 28210^2 + 14289^2 .

It is a cyclic number.

It is not a de Polignac number, because 999979621 - 2¹ = 999979619 is a prime.

Together with 999979619, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 999979621.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (999079621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499989810 + 499989811.

It is an arithmetic number, because the mean of its divisors is an integer number (499989811).

Almost surely, 2^999979621 is an apocalyptic number.

It is an amenable number.

999979621 is a deficient number, since it is larger than the sum of its proper divisors (1).

999979621 is an equidigital number, since it uses as much as digits as its factorization.

999979621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4960116, while the sum is 61.

The square root of 999979621 is about 31622.4543797600. The cubic root of 999979621 is about 999.9932069539.

The spelling of 999979621 in words is "nine hundred ninety-nine million, nine hundred seventy-nine thousand, six hundred twenty-one".