81621394 has 4 divisors (see below), whose sum is σ = 122432094. Its totient is φ = 40810696.

The previous prime is 81621391. The next prime is 81621409. The reversal of 81621394 is 49312618.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 49312618 = 2 ⋅24656309.

It can be written as a sum of positive squares in only one way, i.e., 65820769 + 15800625 = 8113^2 + 3975^2 .

It is not an unprimeable number, because it can be changed into a prime (81621391) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20405347 + ... + 20405350.

Almost surely, 2^81621394 is an apocalyptic number.

81621394 is a deficient number, since it is larger than the sum of its proper divisors (40810700).

81621394 is a wasteful number, since it uses less digits than its factorization.

81621394 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40810699.

The product of its digits is 10368, while the sum is 34.

The square root of 81621394 is about 9034.4559327056. The cubic root of 81621394 is about 433.7784799710.

The spelling of 81621394 in words is "eighty-one million, six hundred twenty-one thousand, three hundred ninety-four".