a, b, c are in arithmetic progression

a || b || c = abc is a 7-digit number

Find the largest 7-digit number obtained in this way.

K.D. BAJPAI

9500991 = 9 || 500 || 991 with common difference 491

9899100 = 98 || 99 || 100 with common difference 1

Paul:

the largest 8-digit number with 3 concatenations

9 || 999 || 1989 with common difference 990.

the largest 9-digit number with 3 concatenations

999 || 998 || 997 common diff of 1

the largest 10-digit number with 3 concatenations

9 || 9999 || 19989 common diff of 9990

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9500991 : 9||500||991 with common difference 491.

9899100 : 98||99||100 with common difference 1.

Nice! And 9899100 > 9500991

Here is the largest 8 digit number with 3 concatenations

9 || 999 ||1989 with common difference 990.

Paul.

The 9 digit one seemed trivial with

999 || 998 || 997 common diff of 1

and the 10 digit one is

9 || 9999 || 19989 common diff of 9990

Paul.