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A087471 Final digit resulting from iterations of the product of the two numbers formed from the alternating digits of n. 5
1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 2, 4, 6, 8, 0, 2, 4, 6, 8, 0, 3, 6, 9, 2, 5, 8, 2, 8, 4, 0, 4, 8, 2, 6, 0, 8, 6, 6, 8, 0, 5, 0, 5, 0, 0, 0, 5, 0, 0, 0, 6, 2, 8, 8, 0, 8, 8, 6, 0, 0, 7, 4, 2, 6, 5, 8, 8, 0, 8, 0, 8, 6, 8, 6, 0, 6, 0, 8, 4, 0, 9, 8, 4, 8, 0, 0, 8, 4, 8, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A087472(n) gives the number of iterations required for Murthy's function, f(n), to reach a single digit. A087473(n) gives the smallest number that requires n iterations of Murthy's function to reach a single digit. The n-th row of triangle A087474 gives the n successive iterations of Murthy's function on A087473(n).

Apart from the undefined a(0), the sequence differs from A031347 first at n=121. [From R. J. Mathar, Sep 11 2008]

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = a(f(n)), where f(n) is Murthy's function: f(1234)=13*24=312, f(12345)=135*24=3240, f(123456)=135*246=33210.

EXAMPLE

a(1234) = a(13*24) = a(312) = a(32*1) = a(32) = a(3*2) = 6.

MATHEMATICA

Table[NestWhile[With[{idn=IntegerDigits[#]}, FromDigits[Take[idn, {1, -1, 2}]] FromDigits[Take[idn, {2, -1, 2}]]]&, n, #>9&], {n, 110}] (* Harvey P. Dale, Dec 05 2014 *)

CROSSREFS

Cf. A087472, A087473, A087474.

Sequence in context: A175420 A062078 A031347 * A128212 A187844 A007954

Adjacent sequences:  A087468 A087469 A087470 * A087472 A087473 A087474

KEYWORD

nonn,base

AUTHOR

Amarnath Murthy and Paul D. Hanna, Sep 11 2003

STATUS

approved

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Last modified June 1 11:51 EDT 2020. Contains 334762 sequences. (Running on oeis4.)