1971949621 has 4 divisors (see below), whose sum is σ = 1974541644. Its totient is φ = 1969357600.

The previous prime is 1971949601. The next prime is 1971949633. The reversal of 1971949621 is 1269491791.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1269491791 = 29 ⋅43775579.

It can be written as a sum of positive squares in 2 ways, for example, as 158382225 + 1813567396 = 12585^2 + 42586^2 .

It is a cyclic number.

It is not a de Polignac number, because 1971949621 - 2²⁵ = 1938395189 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1971949601) 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, 1294870 + ... + 1296391.

It is an arithmetic number, because the mean of its divisors is an integer number (493635411).

Almost surely, 2^1971949621 is an apocalyptic number.

It is an amenable number.

1971949621 is a deficient number, since it is larger than the sum of its proper divisors (2592023).

1971949621 is an equidigital number, since it uses as much as digits as its factorization.

1971949621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2592022.

The product of its digits is 244944, while the sum is 49.

The square root of 1971949621 is about 44406.6393797144. The cubic root of 1971949621 is about 1254.0030857056.

The spelling of 1971949621 in words is "one billion, nine hundred seventy-one million, nine hundred forty-nine thousand, six hundred twenty-one".