MathCastle
Number TheoryHardCircles & Lines

Circles & Lines · Hard problem

A four-digit positive integer has digits d1,d2,d3,d4d_1, d_2, d_3, d_4 (read left to right) that form an arithmetic progression with common difference 22, so d2=d1+2d_2 = d_1+2, d3=d1+4d_3=d_1+4, and d4=d1+6d_4=d_1+6, with d1≥1d_1 \ge 1. How many such four-digit integers are divisible by 1111?