81642551 has 8 divisors (see below), whose sum is σ = 86526000. Its totient is φ = 76768128.

The previous prime is 81642541. The next prime is 81642553. The reversal of 81642551 is 15524618.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81642551 - 2¹⁸ = 81380407 is a prime.

It is a super-2 number, since 2×81642551² = 13331012267575202, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81642553) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 28325 + ... + 31073.

It is an arithmetic number, because the mean of its divisors is an integer number (10815750).

Almost surely, 2^81642551 is an apocalyptic number.

81642551 is a deficient number, since it is larger than the sum of its proper divisors (4883449).

81642551 is a wasteful number, since it uses less digits than its factorization.

81642551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4513.

The product of its digits is 9600, while the sum is 32.

The square root of 81642551 is about 9035.6267629866. The cubic root of 81642551 is about 433.8159564953.

The spelling of 81642551 in words is "eighty-one million, six hundred forty-two thousand, five hundred fifty-one".