840006421 has 2 divisors, whose sum is σ = 840006422. Its totient is φ = 840006420.

The previous prime is 840006407. The next prime is 840006439. The reversal of 840006421 is 124600048.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 644398225 + 195608196 = 25385^2 + 13986^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-840006421 is a prime.

It is a super-2 number, since 2×840006421² = 1411221574642458482, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (840006451) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 420003210 + 420003211.

It is an arithmetic number, because the mean of its divisors is an integer number (420003211).

Almost surely, 2^840006421 is an apocalyptic number.

It is an amenable number.

840006421 is a deficient number, since it is larger than the sum of its proper divisors (1).

840006421 is an equidigital number, since it uses as much as digits as its factorization.

840006421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1536, while the sum is 25.

The square root of 840006421 is about 28982.8642649411. The cubic root of 840006421 is about 943.5412002090.

Adding to 840006421 its reverse (124600048), we get a palindrome (964606469).

The spelling of 840006421 in words is "eight hundred forty million, six thousand, four hundred twenty-one".