21437378561 has 2 divisors, whose sum is σ = 21437378562. Its totient is φ = 21437378560.

The previous prime is 21437378507. The next prime is 21437378563. The reversal of 21437378561 is 16587373412.

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., 19889742961 + 1547635600 = 141031^2 + 39340^2 .

It is a cyclic number.

It is not a de Polignac number, because 21437378561 - 2²² = 21433184257 is a prime.

It is a super-2 number, since 2×21437378561² (a number of 21 digits) contains 22 as substring.

Together with 21437378563, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21437378563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10718689280 + 10718689281.

It is an arithmetic number, because the mean of its divisors is an integer number (10718689281).

Almost surely, 2^21437378561 is an apocalyptic number.

It is an amenable number.

21437378561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21437378561 is an equidigital number, since it uses as much as digits as its factorization.

21437378561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 846720, while the sum is 47.

The spelling of 21437378561 in words is "twenty-one billion, four hundred thirty-seven million, three hundred seventy-eight thousand, five hundred sixty-one".