Arithmetic

Syracuse sequence
Flavius Josephus
Fibonacci sequence

u_n is the sum of the p preceding terms.

p =     u_n :

Prime numbers

crible.c Program C. Table of differences of primes using the sieve of Eratosthene.
Construction of a table of primes (java et javascript)
Search of n-uples of consecutives primes with known differences.
Probable primes
Polynomials
In particular Euler's polynomial n² + n + 41 such that P(0), P(1), ..., P(39) are all primes. The records are Q(n) = 36 n² -810 n + 2753 et Q(44-n) with 45 primes.

Divisors
Prime decomposition
GCD. Bezout identity.
Continued Fractions
Perfect numbers. Amiables pairs
Aliquot sequences
Practical numbers

Is practical ?
Table construct (en java)
n-uples.
Table of practicals or list up to 100000.
prnstewart.c Program (in C language).

Vampire numbers
Like 27 x 81 = 2187 or 12158 x 91067 = 1107192586, they have the same digits that two factors.

Arithmetic bookmarks.