21763751561 has 2 divisors, whose sum is σ = 21763751562. Its totient is φ = 21763751560.

The previous prime is 21763751519. The next prime is 21763751573. The reversal of 21763751561 is 16515736712.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19636697161 + 2127054400 = 140131^2 + 46120^2 .

It is a cyclic number.

It is not a de Polignac number, because 21763751561 - 2²² = 21759557257 is a prime.

It is not a weakly prime, because it can be changed into another prime (21763751161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10881875780 + 10881875781.

It is an arithmetic number, because the mean of its divisors is an integer number (10881875781).

Almost surely, 2^21763751561 is an apocalyptic number.

It is an amenable number.

21763751561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21763751561 is an equidigital number, since it uses as much as digits as its factorization.

21763751561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 264600, while the sum is 44.

The spelling of 21763751561 in words is "twenty-one billion, seven hundred sixty-three million, seven hundred fifty-one thousand, five hundred sixty-one".