1640390421 has 4 divisors (see below), whose sum is σ = 2187187232. Its totient is φ = 1093593612.

The previous prime is 1640390419. The next prime is 1640390471. The reversal of 1640390421 is 1240930461.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1240930461 = 3 ⋅413643487.

It is not a de Polignac number, because 1640390421 - 2¹ = 1640390419 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1640390471) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 273398401 + ... + 273398406.

It is an arithmetic number, because the mean of its divisors is an integer number (546796808).

Almost surely, 2^1640390421 is an apocalyptic number.

It is an amenable number.

1640390421 is a deficient number, since it is larger than the sum of its proper divisors (546796811).

1640390421 is an equidigital number, since it uses as much as digits as its factorization.

1640390421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 546796810.

The product of its (nonzero) digits is 5184, while the sum is 30.

The square root of 1640390421 is about 40501.7335554912. The cubic root of 1640390421 is about 1179.3672804920.

The spelling of 1640390421 in words is "one billion, six hundred forty million, three hundred ninety thousand, four hundred twenty-one".