81907661 has 4 divisors (see below), whose sum is σ = 89353824. Its totient is φ = 74461500.

The previous prime is 81907643. The next prime is 81907681. The reversal of 81907661 is 16670918.

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 a cyclic number.

It is not a de Polignac number, because 81907661 - 2¹⁰ = 81906637 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 (81907681) 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, 3723065 + ... + 3723086.

It is an arithmetic number, because the mean of its divisors is an integer number (22338456).

Almost surely, 2^81907661 is an apocalyptic number.

It is an amenable number.

81907661 is a deficient number, since it is larger than the sum of its proper divisors (7446163).

81907661 is a wasteful number, since it uses less digits than its factorization.

81907661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7446162.

The product of its (nonzero) digits is 18144, while the sum is 38.

The square root of 81907661 is about 9050.2851336298. The cubic root of 81907661 is about 434.2850120922.

It can be divided in two parts, 8190 and 7661, that added together give a palindrome (15851).

The spelling of 81907661 in words is "eighty-one million, nine hundred seven thousand, six hundred sixty-one".