20661551 has 2 divisors, whose sum is σ = 20661552. Its totient is φ = 20661550.

The previous prime is 20661541. The next prime is 20661583. The reversal of 20661551 is 15516602.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20661551 - 2¹⁰ = 20660527 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20661551.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20661541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10330775 + 10330776.

It is an arithmetic number, because the mean of its divisors is an integer number (10330776).

Almost surely, 2^20661551 is an apocalyptic number.

20661551 is a deficient number, since it is larger than the sum of its proper divisors (1).

20661551 is an equidigital number, since it uses as much as digits as its factorization.

20661551 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 20661551 is about 4545.4978825207. The cubic root of 20661551 is about 274.4022321513.

It can be divided in two parts, 20661 and 551, that added together give a palindrome (21212).

The spelling of 20661551 in words is "twenty million, six hundred sixty-one thousand, five hundred fifty-one".