81306621 has 24 divisors (see below), whose sum is σ = 128602656. Its totient is φ = 49091040.

The previous prime is 81306613. The next prime is 81306629. The reversal of 81306621 is 12660318.

81306621 is a `hidden beast` number, since 8 + 1 + 30 + 6 + 621 = 666.

It is an interprime number because it is at equal distance from previous prime (81306613) and next prime (81306629).

It is not a de Polignac number, because 81306621 - 2³ = 81306613 is a prime.

It is a super-2 number, since 2×81306621² = 13221533236875282, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81306629) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 27606 + ... + 30408.

It is an arithmetic number, because the mean of its divisors is an integer number (5358444).

Almost surely, 2^81306621 is an apocalyptic number.

It is an amenable number.

81306621 is a deficient number, since it is larger than the sum of its proper divisors (47296035).

81306621 is a wasteful number, since it uses less digits than its factorization.

81306621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3113 (or 3110 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 81306621 is about 9017.0184096518. The cubic root of 81306621 is about 433.2201392049.

Adding to 81306621 its reverse (12660318), we get a palindrome (93966939).

The spelling of 81306621 in words is "eighty-one million, three hundred six thousand, six hundred twenty-one".