X pas en avant, 1 pas en arrière
Voici les 100 premiers numéros d'une séquence simple: 0,1,0,2,1,4,3,7,6,11,10,16,15,22,21,29,28,37,36,46,45,56,55,67,66,79,78,92,91,106,105,121,120,137,136,154,153,172,171,191,190,211,210,232,231,254,253,277,276,301,300,326,325,352,351,379,378,407,406,436,435,466,465,497,496,529,528,562,561,596,595,631,630,667,666,704,703,742,741,781,780,821,820,862,861,904,903,947,946,991,990,1036,1035,1082,1081,1129,1128,1177,1176,1226 Comment fonctionne cette séquence? n: 0 1 2 3 4 5 6 7 8 9 10 11 12 0, 1-1=0, 2-1=1, 4-1=3, 7-1=6, 11-1=10, 16-1=15, 0+1=1, 0+2=2, 1+3=4, 3+4=7, 6+5=11, 10+6=16, 15+7=22 a(0) = 0 Pour chaque impair n(index 0), c'est …