Number of the day: 641

Blaise Pascal was born on this day 394 years ago.

Properties of the number 641:

641 is a cyclic number.
641 and 643 form a twin prime pair.
641 has 7 antidivisors and 640 totatives.
641 has a prime digit sum 11 in base 10.
641 has sum of divisors equal to 642 which is a sphenic number.
Reversing the decimal digits of 641 results in a semiprime.
641 = 321² - 320² is the difference of 2 nonnegative squares in 1 way.
641 is the difference of 2 positive pentagonal numbers in 1 way.
641 = 4² + 25² is the sum of 2 positive squares in 1 way.
641 = 6² + 11² + 22² is the sum of 3 positive squares.
641² = 200² + 609² is the sum of 2 positive squares in 1 way.
641² is the sum of 3 positive squares.
641 is a proper divisor of 487⁴ - 1.
641 is an emirp in (at least) the following bases: 3, 9, 11, 13, 15, 22, 27, 29, 36, 37, 45, 47, 48, 53, 54, 57, 59, 61, 71, 75, 77, 79, 82, 83, 85, 86, 87, 88, 89, and 90.
641 is palindromic in (at least) the following bases: 20, -12, -13, -32, -40, -64, and -80.
641 in base 11 = 533 and consists of only the digits '3' and '5'.
641 in base 12 = 455 and consists of only the digits '4' and '5'.
641 in base 14 = 33b and consists of only the digits '3' and 'b'.
641 in base 19 = 1ee and consists of only the digits '1' and 'e'.
641 in base 20 = 1c1 and consists of only the digits '1' and 'c'.

The number 641 belongs to the following On-Line Encyclopedia of Integer Sequences (OEIS) sequences (among others):

Sequence numbers and descriptions below are taken from OEIS.
A001097: Twin primes.
A001359: Lesser of twin primes.
A005384: Sophie Germain primes p: 2p+1 is also prime.
A005846: Primes of the form n^2 + n + 41.
A007519: Primes of form 8n+1, that is, primes congruent to 1 mod 8.
A023201: Sexy primes: numbers n such that n and n + 6 are both prime.
A104272: Ramanujan primes R_n: a(n) is the smallest number such that if x >= a(n), then pi(x) - pi(x/2) >= n, where pi(x) is the number of primes <= x.
A106856: Primes of the form x^2+xy+2y^2, with x and y nonnegative.
A212959: Number of (w,x,y) such that w,x,y are all in {0,...,n} and |w-x| = |x-y|.
A235266: Primes whose base 2 representation is also the base 3 representation of a prime.