81219217666 has 16 divisors (see below), whose sum is σ = 122892950304. Its totient is φ = 40256388864.

The previous prime is 81219217661. The next prime is 81219217669. The reversal of 81219217666 is 66671291218.

It is a happy number.

It is a super-2 number, since 2×81219217666² (a number of 23 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81219217661) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 262516 + ... + 480991.

It is an arithmetic number, because the mean of its divisors is an integer number (7680809394).

Almost surely, 2^81219217666 is an apocalyptic number.

81219217666 is a deficient number, since it is larger than the sum of its proper divisors (41673732638).

81219217666 is a wasteful number, since it uses less digits than its factorization.

81219217666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 743985.

The product of its digits is 435456, while the sum is 49.

The spelling of 81219217666 in words is "eighty-one billion, two hundred nineteen million, two hundred seventeen thousand, six hundred sixty-six".