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A085307 a(1) = 1; for n > 1, concatenate distinct prime factors of n in decreasing order. 7
1, 2, 3, 2, 5, 32, 7, 2, 3, 52, 11, 32, 13, 72, 53, 2, 17, 32, 19, 52, 73, 112, 23, 32, 5, 132, 3, 72, 29, 532, 31, 2, 113, 172, 75, 32, 37, 192, 133, 52, 41, 732, 43, 112, 53, 232, 47, 32, 7, 52, 173, 132, 53, 32, 115, 72, 193, 292, 59, 532, 61, 312, 73, 2, 135, 1132, 67 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

n and a(n) have the same parity.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..20000

FORMULA

Algorithm:

1. factorize n;

2. order prime factors by decreasing size;

3. concatenate prime factors and interpret the result as a decimal number.

EXAMPLE

m = 100 = 2*2*5*5 -> {2,5} -> {5,2} -> 52 = a(100);

a(510510) = 1713117532, while A084317(510510) = 2357111317.

MAPLE

with(numtheory):

a:= n-> parse(cat(`if`(n=1, 1, sort([factorset(n)[]], `>`)[]))):

seq(a(n), n=1..100);  # Alois P. Heinz, May 02 2016

MATHEMATICA

f[n_] := FromDigits[ Flatten[ IntegerDigits /@ Reverse[ Flatten[ Table[ # [[1]], {1}] & /@ FactorInteger[n]]]]]; Table[ f[n], {n, 1, 70}]

Table[FromDigits[Flatten[IntegerDigits/@Reverse[FactorInteger[n][[All, 1]]]]], {n, 90}] (* Harvey P. Dale, Oct 10 2017 *)

CROSSREFS

In A084317 the order of factors is increasing.

Cf. A084317, A084318, A084319, A085308, A085309, A084796, A084797.

Sequence in context: A084317 A037279 A163591 * A078599 A183103 A183105

Adjacent sequences:  A085304 A085305 A085306 * A085308 A085309 A085310

KEYWORD

base,look,nonn

AUTHOR

Labos Elemer, Jun 27 2003

EXTENSIONS

Edited by Robert G. Wilson v, Jul 15 2003

STATUS

approved

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Last modified June 17 14:09 EDT 2019. Contains 324185 sequences. (Running on oeis4.)