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  2. Happy number - Wikipedia

    en.wikipedia.org/wiki/Happy_number

    The examples below implement the perfect digital invariant function for = and a default base = described in the definition of happy given at the top of this article, repeatedly; after each time, they check for both halt conditions: reaching 1, and repeating a number. A simple test in Python to check if a number is happy:

  3. Centered square number - Wikipedia

    en.wikipedia.org/wiki/Centered_square_number

    Example: as shown in the following figure of Floyd's triangle, 25 is a centered square number, and is the sum of the square 16 (yellow rhombus formed by shearing a square) and of the next smaller square, 9 (sum of two blue triangles): Centered square numbers (in red) are in the center of odd rows of Floyd's triangle.

  4. Python syntax and semantics - Wikipedia

    en.wikipedia.org/wiki/Python_syntax_and_semantics

    Introduced in Python 2.2 as an optional feature and finalized in version 2.3, generators are Python's mechanism for lazy evaluation of a function that would otherwise return a space-prohibitive or computationally intensive list. This is an example to lazily generate the prime numbers:

  5. Marching squares - Wikipedia

    en.wikipedia.org/wiki/Marching_squares

    In computer graphics, marching squares is an algorithm that generates contours for a two-dimensional scalar field (rectangular array of individual numerical values). A similar method can be used to contour 2D triangle meshes. The contours can be of two kinds: Isolines – lines following a single data level, or isovalue.

  6. Integer sequence - Wikipedia

    en.wikipedia.org/wiki/Integer_sequence

    An integer sequence is computable if there exists an algorithm that, given n, calculates a n, for all n > 0. The set of computable integer sequences is countable.The set of all integer sequences is uncountable (with cardinality equal to that of the continuum), and so not all integer sequences are computable.

  7. Middle-square method - Wikipedia

    en.wikipedia.org/wiki/Middle-square_method

    Consider the following: If a 3-digit number is squared, it can yield a 6-digit number (e.g. 540 2 = 291600). If there were to be middle 3 digits, that would leave 6 − 3 = 3 digits to be distributed to the left and right of the middle.

  8. Sum of two squares theorem - Wikipedia

    en.wikipedia.org/wiki/Sum_of_two_squares_theorem

    Of the primes occurring in this decomposition, 2, 5, and 7, only 7 is congruent to 3 modulo 4. Its exponent in the decomposition, 2, is even. Therefore, the theorem states that it is expressible as the sum of two squares. Indeed, 2450 = 7 2 + 49 2. The prime decomposition of the number 3430 is 2 · 5 · 7 3. This time, the exponent of 7 in the ...

  9. Powerful number - Wikipedia

    en.wikipedia.org/wiki/Powerful_number

    A powerful number is a positive integer m such that for every prime number p dividing m, p 2 also divides m. Equivalently, a powerful number is the product of a square and a cube, that is, a number m of the form m = a 2 b 3, where a and b are positive integers. Powerful numbers are also known as squareful, square-full, or 2-full.