420021781 has 2 divisors, whose sum is σ = 420021782. Its totient is φ = 420021780.

The previous prime is 420021709. The next prime is 420021787. The reversal of 420021781 is 187120024.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 217415025 + 202606756 = 14745^2 + 14234^2 .

It is a cyclic number.

It is not a de Polignac number, because 420021781 - 2⁹ = 420021269 is a prime.

It is a super-2 number, since 2×420021781² = 352836593028823922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (420021787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 210010890 + 210010891.

It is an arithmetic number, because the mean of its divisors is an integer number (210010891).

Almost surely, 2^420021781 is an apocalyptic number.

It is an amenable number.

420021781 is a deficient number, since it is larger than the sum of its proper divisors (1).

420021781 is an equidigital number, since it uses as much as digits as its factorization.

420021781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 420021781 is about 20494.4329270170. The cubic root of 420021781 is about 748.9001841433.

The spelling of 420021781 in words is "four hundred twenty million, twenty-one thousand, seven hundred eighty-one".