20131561 has 2 divisors, whose sum is σ = 20131562. Its totient is φ = 20131560.

The previous prime is 20131549. The next prime is 20131571. The reversal of 20131561 is 16513102.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19855936 + 275625 = 4456^2 + 525^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20131561 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20131541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10065780 + 10065781.

It is an arithmetic number, because the mean of its divisors is an integer number (10065781).

Almost surely, 2^20131561 is an apocalyptic number.

It is an amenable number.

20131561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20131561 is an equidigital number, since it uses as much as digits as its factorization.

20131561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 180, while the sum is 19.

The square root of 20131561 is about 4486.8208121118. The cubic root of 20131561 is about 272.0356471807.

Adding to 20131561 its reverse (16513102), we get a palindrome (36644663).

The spelling of 20131561 in words is "twenty million, one hundred thirty-one thousand, five hundred sixty-one".