21630761 has 2 divisors, whose sum is σ = 21630762. Its totient is φ = 21630760.

The previous prime is 21630733. The next prime is 21630769. The reversal of 21630761 is 16703612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19009600 + 2621161 = 4360^2 + 1619^2 .

It is a cyclic number.

It is not a de Polignac number, because 21630761 - 2¹⁸ = 21368617 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is equal to p_1367342 and since 21630761 and 1367342 have the same sum of digits, it is a Honaker prime.

It is a plaindrome in base 11.

It is a self number, because there is not a number n which added to its sum of digits gives 21630761.

It is not a weakly prime, because it can be changed into another prime (21630769) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10815380 + 10815381.

It is an arithmetic number, because the mean of its divisors is an integer number (10815381).

Almost surely, 2^21630761 is an apocalyptic number.

It is an amenable number.

21630761 is a deficient number, since it is larger than the sum of its proper divisors (1).

21630761 is an equidigital number, since it uses as much as digits as its factorization.

21630761 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1512, while the sum is 26.

The square root of 21630761 is about 4650.8881947430. Note that the first 3 decimals coincide. The cubic root of 21630761 is about 278.6274709326.

The spelling of 21630761 in words is "twenty-one million, six hundred thirty thousand, seven hundred sixty-one".