81202771521 has 45 divisors (see below), whose sum is σ = 122694592449. Its totient is φ = 51751197288.

The previous prime is 81202771513. The next prime is 81202771541. The reversal of 81202771521 is 12517720218.

The square root of 81202771521 is 284961.

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

81202771521 is a `hidden beast` number, since 8 + 120 + 2 + 7 + 7 + 1 + 521 = 666.

It is not a de Polignac number, because 81202771521 - 2³ = 81202771513 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81202771511) by changing a digit.

It is a polite number, since it can be written in 44 ways as a sum of consecutive naturals, for example, 1727718520 + ... + 1727718566.

Almost surely, 2^81202771521 is an apocalyptic number.

81202771521 is the 284961-st square number.

81202771521 is the 142481-st centered octagonal number.

It is an amenable number.

81202771521 is a deficient number, since it is larger than the sum of its proper divisors (41491820928).

81202771521 is an frugal number, since it uses more digits than its factorization.

81202771521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 280 (or 93 counting only the distinct ones).

The product of its (nonzero) digits is 15680, while the sum is 36.

Multiplying 81202771521 by its sum of digits (36), we get a square (2923299774756 = 1709766²).

The spelling of 81202771521 in words is "eighty-one billion, two hundred two million, seven hundred seventy-one thousand, five hundred twenty-one".