81401781 has 4 divisors (see below), whose sum is σ = 108535712. Its totient is φ = 54267852.

The previous prime is 81401777. The next prime is 81401783. The reversal of 81401781 is 18710418.

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.

It is not a de Polignac number, because 81401781 - 2² = 81401777 is a prime.

It is a super-2 number, since 2×81401781² = 13252499899943922, 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 (81401783) 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, 13566961 + ... + 13566966.

It is an arithmetic number, because the mean of its divisors is an integer number (27133928).

Almost surely, 2^81401781 is an apocalyptic number.

It is an amenable number.

81401781 is a deficient number, since it is larger than the sum of its proper divisors (27133931).

81401781 is a wasteful number, since it uses less digits than its factorization.

81401781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27133930.

The product of its (nonzero) digits is 1792, while the sum is 30.

The square root of 81401781 is about 9022.2935554104. The cubic root of 81401781 is about 433.3890846744.

The spelling of 81401781 in words is "eighty-one million, four hundred one thousand, seven hundred eighty-one".