81155421 has 6 divisors (see below), whose sum is σ = 117224510. Its totient is φ = 54103608.

The previous prime is 81155411. The next prime is 81155423. The reversal of 81155421 is 12455118.

81155421 is a `hidden beast` number, since 8 + 115 + 542 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 46049796 + 35105625 = 6786^2 + 5925^2 .

It is not a de Polignac number, because 81155421 - 2¹⁵ = 81122653 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 (81155423) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4508626 + ... + 4508643.

Almost surely, 2^81155421 is an apocalyptic number.

It is an amenable number.

81155421 is a deficient number, since it is larger than the sum of its proper divisors (36069089).

81155421 is a wasteful number, since it uses less digits than its factorization.

81155421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9017275 (or 9017272 counting only the distinct ones).

The product of its digits is 1600, while the sum is 27.

The square root of 81155421 is about 9008.6303620473. The cubic root of 81155421 is about 432.9514299251.

The spelling of 81155421 in words is "eighty-one million, one hundred fifty-five thousand, four hundred twenty-one".