1621928151981 has 12 divisors (see below), whose sum is σ = 2350175601852. Its totient is φ = 1077874437696.

The previous prime is 1621928151947. The next prime is 1621928152021. The reversal of 1621928151981 is 1891518291261.

1621928151981 is a `hidden beast` number, since 1 + 6 + 21 + 9 + 28 + 1 + 519 + 81 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 926762409225 + 695165742756 = 962685^2 + 833766^2 .

It is not a de Polignac number, because 1621928151981 - 2¹⁵ = 1621928119213 is a prime.

It is a super-2 number, since 2×1621928151981² (a number of 25 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1621928151941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 284246736 + ... + 284252441.

It is an arithmetic number, because the mean of its divisors is an integer number (195847966821).

Almost surely, 2^{1621928151981} is an apocalyptic number.

It is an amenable number.

1621928151981 is a deficient number, since it is larger than the sum of its proper divisors (728247449871).

1621928151981 is a wasteful number, since it uses less digits than its factorization.

1621928151981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 568499500 (or 568499497 counting only the distinct ones).

The product of its digits is 622080, while the sum is 54.

The spelling of 1621928151981 in words is "one trillion, six hundred twenty-one billion, nine hundred twenty-eight million, one hundred fifty-one thousand, nine hundred eighty-one".