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A260704 Number of pairs of distinct divisors of A260703(n) having the property that the reversal of one is equal to the other. 3
1, 1, 2, 1, 2, 1, 1, 1, 3, 1, 1, 1, 1, 3, 1, 1, 1, 1, 2, 3, 1, 2, 1, 2, 2, 2, 1, 2, 1, 1, 4, 1, 2, 1, 1, 2, 2, 1, 2, 2, 1, 2, 1, 3, 1, 1, 1, 1, 1, 2, 4, 1, 1, 2, 2, 3, 1, 1, 1, 2, 2, 1, 4, 1, 1, 1, 2, 1, 1, 4, 1, 1, 1, 2, 2, 2, 1, 3, 1, 2, 3, 2, 1, 3, 2, 1, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

A260703: numbers having at least two divisors such that the reversal of one is equal to the other.

LINKS

Michel Lagneau, Table of n, a(n) for n = 1..10000

EXAMPLE

a(9)=3 because A260703(9) = 336 and the set of the divisors of 336, {1, 2, 3, 4, 6, 7, 8, 12, 14, 16, 21, 24, 28, 42, 48, 56, 84, 112, 168, 336} contains 3 pairs (12, 21), (24, 42) and (48, 84) with the property: 21 = reversal(12), 42 = reversal(24) and 84 = reversal(48).

MAPLE

with(numtheory):nn:=5000:

for n from 1 to nn do:

it:=0:d:=divisors(n):d0:=nops(d):

  for i from 1 to d0 do:

   dd:=d[i]:y:=convert(dd, base, 10):n1:=length(dd):

   s:=sum('y[j]*10^(n1-j)', 'j'=1..n1):

    for k from i+1 to d0 do:

     if s=d[k]

     then

     it:=it+1:

     else fi:

    od:

    od:

    if it>0

    then

    printf(`%d, `, it):

    else fi:

od:

MATHEMATICA

f[n_] := Block[{d = Select[Divisors@n, IntegerLength@# > 1 &], palQ, r}, palQ[x_] := Reverse@ # == # &@ IntegerDigits@ x; r = FromDigits@ Reverse@ IntegerDigits@ # & /@ d; Length@ Select[Intersection[d, r], ! palQ@ # &]/2]; f /@ Range@ 3000 /. 0 -> Nothing (* Michael De Vlieger, Nov 17 2015 *)

CROSSREFS

Cf. A000005, A027750, A083815, A260703, A260705.

Sequence in context: A176510 A061342 A104639 * A161223 A145672 A175024

Adjacent sequences:  A260701 A260702 A260703 * A260705 A260706 A260707

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Nov 17 2015

STATUS

approved

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Last modified June 20 19:36 EDT 2019. Contains 324234 sequences. (Running on oeis4.)