even more math

[Emanuel Berg]

I saw this when we did the lambda bindings, it holds from
0 to 99 at least :)

;;; -*- lexical-binding: t -*-
;;
;; this file:
;;   https://dataswamp.org/~incal/emacs-init/geh.el

(require 'cl-lib)

(defun arith-sum (n)
  (cl-loop
    with sum = 0
    for i from 1 to (1- n)
    do (cl-incf sum i)
    finally return sum) )

(defun digs (n)
  (* n (1- n)) )

(cl-loop
  for i from 0 to 99
  while (= (digs i) (* 2 (arith-sum i)))
  finally return i)

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