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 A116444 Numbers k which when sandwiched between two 9's give a multiple of k. 9
 1, 3, 9, 11, 13, 21, 33, 39, 63, 77, 91, 99, 137, 219, 411, 657, 9091, 29703, 89109, 909091, 5882353, 10989011, 12145749, 12987013, 14354067, 20979021, 22556391, 32967033, 36437247, 38961039, 43062201, 52631579, 62937063, 67669173, 76923077, 90909091, 98901099 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Michael S. Branicky, Table of n, a(n) for n = 1..5016 EXAMPLE 411 belongs since 94119 is a multiple of 411 (411*229). MATHEMATICA f[k_, d_] := Flatten@Table[Select[Divisors[k*(10^(i + 1) + 1)], IntegerLength[ # ] == i &], {i, d}]; f[9, 8] (* Ray Chandler, May 11 2007 *) PROG (PARI) for(d=1, 10, fordiv(9*10^(d+1)+9, a, if(#Str(a)==d, print1(a", ")))) /* Martin Fuller, May 10 2007 */ (Python) from sympy import isprime from itertools import count, islice def agen(): # generator of terms yield from [1, 3, 9] for k in count(2): t = 9*(10**(k+1) + 1) yield from (t//i for i in range(900, 90, -1) if t%i == 0) print(list(islice(agen(), 38))) # Michael S. Branicky, Mar 26 2023 CROSSREFS Cf. A116436, A116437, A116438, A116439, A116440, A116441, A116442, A116443. Sequence in context: A235583 A287333 A174813 * A215820 A065136 A075720 Adjacent sequences: A116441 A116442 A116443 * A116445 A116446 A116447 KEYWORD base,nonn AUTHOR Giovanni Resta, Feb 15 2006 EXTENSIONS Corrected by Martin Fuller, May 10 2007 a(35) and beyond from Michael S. Branicky, Mar 26 2023 STATUS approved

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Last modified December 7 21:37 EST 2023. Contains 367662 sequences. (Running on oeis4.)