81413779561 has 9 divisors (see below), whose sum is σ = 84326527831. Its totient is φ = 78598418584.

The previous prime is 81413779549. The next prime is 81413779567. The reversal of 81413779561 is 16597731418.

The square root of 81413779561 is 285331.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 42691411161 + 38722368400 = 206619^2 + 196780^2 .

It is not a de Polignac number, because 81413779561 - 2²⁹ = 80876908649 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81413779499 and 81413779508.

It is not an unprimeable number, because it can be changed into a prime (81413779567) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 8269680 + ... + 8279518.

Almost surely, 2^81413779561 is an apocalyptic number.

81413779561 is the 285331-st square number.

81413779561 is the 142666-th centered octagonal number.

It is an amenable number.

81413779561 is a deficient number, since it is larger than the sum of its proper divisors (2912748270).

81413779561 is an frugal number, since it uses more digits than its factorization.

81413779561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19736 (or 9868 counting only the distinct ones).

The product of its digits is 1270080, while the sum is 52.

The spelling of 81413779561 in words is "eighty-one billion, four hundred thirteen million, seven hundred seventy-nine thousand, five hundred sixty-one".