21121153561 has 2 divisors, whose sum is σ = 21121153562. Its totient is φ = 21121153560.

The previous prime is 21121153517. The next prime is 21121153577. The reversal of 21121153561 is 16535112112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11638094400 + 9483059161 = 107880^2 + 97381^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21121153561 is a prime.

It is a super-2 number, since 2×21121153561² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21121153591) 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 as a sum of consecutive naturals, namely, 10560576780 + 10560576781.

It is an arithmetic number, because the mean of its divisors is an integer number (10560576781).

Almost surely, 2^21121153561 is an apocalyptic number.

It is an amenable number.

21121153561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21121153561 is an equidigital number, since it uses as much as digits as its factorization.

21121153561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1800, while the sum is 28.

Adding to 21121153561 its reverse (16535112112), we get a palindrome (37656265673).

The spelling of 21121153561 in words is "twenty-one billion, one hundred twenty-one million, one hundred fifty-three thousand, five hundred sixty-one".