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A116440 Numbers n which when sandwiched between two 5's give a multiple of n. 0
1, 5, 11, 13, 35, 55, 65, 77, 91, 137, 365, 685, 9091, 49505, 909091, 5882353, 10989011, 12987013, 20242915, 23923445, 34965035, 37593985, 52631579, 54945055, 64935065, 76923077, 90909091, 495049505, 1976284585, 4132231405 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

All terms must be odd. - Harvey P. Dale, Jul 29 2015

LINKS

Table of n, a(n) for n=1..30.

EXAMPLE

137 belongs since 51375 is a multiple 137 (137*375).

MAPLE

a:=proc(n) local nn: nn:=convert(n, base, 10): if type((5+10*n+5*10^(nops(nn)+1))/n, integer)=true then n else fi end: seq(a(n), n=1..10000); # Emeric Deutsch, Feb 28 2006

MATHEMATICA

f[k_, d_] := Flatten@Table[Select[Divisors[k*(10^(i + 1) + 1)], IntegerLength[ # ] == i &], {i, d}]; f[5, 10] (* Ray Chandler *)

CROSSREFS

Cf. A116436, A116437, A116438, A116439, A116441, A116442, A116443, A116444.

Sequence in context: A098973 A125742 A269844 * A098720 A115091 A034924

Adjacent sequences:  A116437 A116438 A116439 * A116441 A116442 A116443

KEYWORD

base,nonn

AUTHOR

Giovanni Resta, Feb 15 2006

STATUS

approved

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Last modified June 19 19:11 EDT 2019. Contains 324222 sequences. (Running on oeis4.)