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A123132 Describe prime factorization of n ( primes in ascending order and with repetition) (method A - initial term is 2). 3
12, 13, 22, 15, 1213, 17, 32, 23, 1215, 111, 2213, 113, 1217, 1315, 42, 117, 1223, 119, 2215, 1317, 12111, 123, 3213, 25, 12113, 33, 2217, 129, 121315, 131, 52, 13111, 12117, 1517, 2223, 137, 12119, 13113, 3215, 141, 121317, 143, 22111, 2315, 12123 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

Method A = 'frequency' followed by 'digit'-indication. Say 'what you see' in prime factors of n, n>1.

First fixed point is a(25) = 25. - Paolo P. Lava, Jun 29 2017

LINKS

Paolo P. Lava, Table of n, a(n) for n = 2..10000

A. Frank & P. Jacqueroux, International Contest, 2001.

EXAMPLE

2 has "one 2" in its prime decomposition, so a(2)=12.

3 has "one 3" in its prime decomposition, so a(3)=13.

4=2*2 has "two 2" in its prime decomposition, so a(4)=22.

5 has "one 5" in its prime decomposition, so a(5)=15.

6=2*3 has "one 2 and one 3" in its prime decomposition, so a(6)=1213.

.....

MATHEMATICA

a[n_] := FromDigits@ Flatten@ IntegerDigits[ Reverse /@ FactorInteger@ n]; a/@ Range[2, 30] (* Giovanni Resta, Jun 16 2013 *)

PROG

(PARI) for(n=2, 25, factn=factor(n); for(i=1, omega(n), print1(factn[i, 2], factn[i, 1])); print1(", "))

(PARI) a(n) = my(factn=factor(n), sout = ""); for(i=1, omega(n), sout = concat(sout, Str(factn[i, 2])); sout = concat(sout, Str(factn[i, 1]))); eval(sout); \\ Michel Marcus, Jun 29 2017

CROSSREFS

Cf. A006751, A027746, A063850.

Sequence in context: A105733 A035123 A140212 * A050840 A118068 A108710

Adjacent sequences:  A123129 A123130 A123131 * A123133 A123134 A123135

KEYWORD

nonn,base

AUTHOR

Herman Jamke (hermanjamke(AT)fastmail.fm), Sep 30 2006

STATUS

approved

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Last modified December 10 16:44 EST 2018. Contains 318049 sequences. (Running on oeis4.)