81517621 has 2 divisors, whose sum is σ = 81517622. Its totient is φ = 81517620.

The previous prime is 81517607. The next prime is 81517633. The reversal of 81517621 is 12671518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 64625521 + 16892100 = 8039^2 + 4110^2 .

It is a cyclic number.

It is not a de Polignac number, because 81517621 - 2¹³ = 81509429 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81017621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40758810 + 40758811.

It is an arithmetic number, because the mean of its divisors is an integer number (40758811).

Almost surely, 2^81517621 is an apocalyptic number.

It is an amenable number.

81517621 is a deficient number, since it is larger than the sum of its proper divisors (1).

81517621 is an equidigital number, since it uses as much as digits as its factorization.

81517621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3360, while the sum is 31.

The square root of 81517621 is about 9028.7109268156. The cubic root of 81517621 is about 433.5945674674.

The spelling of 81517621 in words is "eighty-one million, five hundred seventeen thousand, six hundred twenty-one".