405688021 has 2 divisors, whose sum is σ = 405688022. Its totient is φ = 405688020.

The previous prime is 405687977. The next prime is 405688033. The reversal of 405688021 is 120886504.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 399000625 + 6687396 = 19975^2 + 2586^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-405688021 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (405688061) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 202844010 + 202844011.

It is an arithmetic number, because the mean of its divisors is an integer number (202844011).

Almost surely, 2^405688021 is an apocalyptic number.

It is an amenable number.

405688021 is a deficient number, since it is larger than the sum of its proper divisors (1).

405688021 is an equidigital number, since it uses as much as digits as its factorization.

405688021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 15360, while the sum is 34.

The square root of 405688021 is about 20141.6985629316. The cubic root of 405688021 is about 740.2823496446.

The spelling of 405688021 in words is "four hundred five million, six hundred eighty-eight thousand, twenty-one".