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 A268517 Three-digit numbers, starting with 321, such that when written in a table with three columns, there are arithmetic progressions modulo 10 down the diagonals, with steps of 1, 2 and 3 respectively. 0
 321, 444, 675, 680, 370, 268, 949, 206, 851, 208, 132, 444, 567, 68, 37, 826, 994, 620, 185, 820, 213, 444, 756, 806, 703, 682, 499, 62, 518, 82, 321, 444, 675, 680, 370, 268, 949, 206, 851, 208, 132, 444, 567, 68, 37, 826, 994, 620, 185, 820, 213, 444, 756, 806 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Repeats after 30 terms. - Chai Wah Wu, Feb 08 2016 REFERENCES GCHQ Director's Christmas Puzzles for 2015. LINKS Table of n, a(n) for n=0..53. GCHQ, Solutions to Director's Christmas Puzzles for 2015 EXAMPLE The table begins 3 2 1 4 4 4 6 7 5 6 8 0 3 7 0 2 6 8 9 4 9 2 0 6 8 5 1 2 0 8 ... and one can see the three arithmetic progressions down the diagonals: 3, 4, 5, 6, ...; 2, 4, 6, 8, ...; 1, 4, 7, 0, ... . PROG (Python) from __future__ import division A268517_list = [321] for i in range(10**4): a = A268517_list[-1] A268517_list.append(((a+1+(2-i)%3) % 10)*100 + ((a//100+1+(-i)%3) % 10)*10 + ((a//10+1+(1-i)%3) % 10)) # Chai Wah Wu, Feb 08 2016 CROSSREFS Sequence in context: A351994 A261262 A308527 * A228226 A004927 A074350 Adjacent sequences: A268514 A268515 A268516 * A268518 A268519 A268520 KEYWORD nonn,base AUTHOR N. J. A. Sloane, Feb 08 2016 EXTENSIONS More terms from Chai Wah Wu, Feb 08 2016 STATUS approved

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Last modified June 3 18:44 EDT 2023. Contains 363116 sequences. (Running on oeis4.)