20511681961 has 9 divisors (see below), whose sum is σ = 20644727799. Its totient is φ = 20379490824.

The previous prime is 20511681947. The next prime is 20511681973. The reversal of 20511681961 is 16918611502.

The square root of 20511681961 is 143219.

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., 20097315225 + 414366736 = 141765^2 + 20356^2 .

It is a de Polignac number, because none of the positive numbers 2^k-20511681961 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20511681901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 28213780 + ... + 28214506.

Almost surely, 2^20511681961 is an apocalyptic number.

20511681961 is the 143219-th square number.

20511681961 is the 71610-th centered octagonal number.

It is an amenable number.

20511681961 is a deficient number, since it is larger than the sum of its proper divisors (133045838).

20511681961 is an frugal number, since it uses more digits than its factorization.

20511681961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1848 (or 924 counting only the distinct ones).

The product of its (nonzero) digits is 25920, while the sum is 40.

The spelling of 20511681961 in words is "twenty billion, five hundred eleven million, six hundred eighty-one thousand, nine hundred sixty-one".