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 A359925 Numbers with easy multiplication table - the first 9 multiples of these numbers can be derived by either incrementing or decrementing the corresponding digits from the previous multiple. 1
 1, 9, 11, 89, 91, 109, 111, 889, 891, 909, 911, 1089, 1091, 1109, 1111, 8889, 8891, 8909, 8911, 9089, 9091, 9109, 9111, 10889, 10891, 10909, 10911, 11089, 11091, 11109, 11111, 88889, 88891, 88909, 88911, 89089, 89091, 89109, 89111, 90889, 90891, 90909, 90911 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS This is also the list of numbers having exactly one dot or one antidot in each box in the Decimal Exploding Dots notation. LINKS Table of n, a(n) for n=1..43. Global Math Week, Exploding Dots. Gevorg Hmayakyan, Generalizing a Trig Identity [mentions this sequence] FORMULA a(n) = 10*a(floor(n/2))+2*(n mod 2)-1 for n>0, a(0)=0. - Alois P. Heinz, Jan 25 2023 a(n) = 2*A256290(n-1) + 1 for n>1. - Hugo Pfoertner, Jan 28 2023 EXAMPLE a(4) = 89. The first nine multiples of 89 are {089, 178, 267, 356, 445, 534, 623, 712, 801}. The digits in the hundreds place increment by 1, while the digits in the tens and units place decrement by 1. In the Decimal Exploding Dots notation, 89 is represented as DOT-ANTIDOT-ANTIDOT = 100 - 10 - 1 = 89 MAPLE a:= proc(n) option remember; `if`(n=0, 0, 10*a(iquo(n, 2, 'm'))+2*m-1) end: seq(a(n), n=1..44); # Alois P. Heinz, Jan 25 2023 CROSSREFS Cf. A006257, A147991, A147992, A153777, A147993, A256290. Column k=10 of A360099. Sequence in context: A195992 A108687 A038301 * A277998 A289288 A137016 Adjacent sequences: A359922 A359923 A359924 * A359926 A359927 A359928 KEYWORD nonn,base AUTHOR Kiran Ananthpur Bacche, Jan 25 2023 STATUS approved

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Last modified June 7 20:32 EDT 2023. Contains 363157 sequences. (Running on oeis4.)