71639821 has 4 divisors (see below), whose sum is σ = 78152544. Its totient is φ = 65127100.

The previous prime is 71639809. The next prime is 71639837. The reversal of 71639821 is 12893617.

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: 12893617 = 11 ⋅1172147.

It is a cyclic number.

It is not a de Polignac number, because 71639821 - 2²³ = 63251213 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 (71639221) 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, 3256345 + ... + 3256366.

It is an arithmetic number, because the mean of its divisors is an integer number (19538136).

Almost surely, 2^71639821 is an apocalyptic number.

It is an amenable number.

71639821 is a deficient number, since it is larger than the sum of its proper divisors (6512723).

71639821 is a wasteful number, since it uses less digits than its factorization.

71639821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6512722.

The product of its digits is 18144, while the sum is 37.

The square root of 71639821 is about 8464.0310136483. The cubic root of 71639821 is about 415.3218986042.

The spelling of 71639821 in words is "seventy-one million, six hundred thirty-nine thousand, eight hundred twenty-one".