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A286610 Restricted growth sequence computed for Euler totient function phi, A000010. 10
1, 1, 2, 2, 3, 2, 4, 3, 4, 3, 5, 3, 6, 4, 7, 7, 8, 4, 9, 7, 6, 5, 10, 7, 11, 6, 9, 6, 12, 7, 13, 8, 11, 8, 14, 6, 15, 9, 14, 8, 16, 6, 17, 11, 14, 10, 18, 8, 17, 11, 19, 14, 20, 9, 16, 14, 15, 12, 21, 8, 22, 13, 15, 19, 23, 11, 24, 19, 25, 14, 26, 14, 27, 15, 16, 15, 22, 14, 28, 19, 29, 16, 30, 14, 31, 17, 32, 16, 33, 14, 27, 25, 22, 18, 27, 19, 34, 17, 22 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

EXAMPLE

Construction: we start with a(1)=1 for phi(1)=1 (where phi = A000010), and then after, for all n > 1, whenever the value of phi(n) has not been encountered before, we set a(n) to the least natural number k not already in sequence among a(1) .. a(n-1), otherwise [whenever phi(n) = phi(m), for some m < n], we set a(n) = a(m), i.e., to the same value that was assigned to a(m).

For n=2, phi(2) = 1, which value was already encountered as phi(1), thus we set also a(2) = 1.

For n=3, phi(3) = 2, which has not been encountered before, thus we allot for a(3) the least so far unused number, which is 2, thus a(3) = 2.

For n=4, phi(4) = 2, which was already encountered as at n=3 for the first time, thus we set a(4) = a(3) = 2.

For n=5, phi(5) = 4, which has not been encountered before, thus we allot for a(5) the least so far unused number, which is now 3, thus a(5) = 3.

MATHEMATICA

With[{nn = 99}, Function[s, Table[Position[Keys@ s, k_ /; MemberQ[k, n]][[1, 1]], {n, nn}]]@ Map[#1 -> #2 & @@ # &, Transpose@ {Values@ #, Keys@ #}] &@ PositionIndex@ Array[EulerPhi, nn]] (* Michael De Vlieger, May 12 2017, Version 10 *)

PROG

(PARI)

rgs_transform(invec) = { my(occurrences = Map(), outvec = vector(length(invec)), u=1); for(i=1, length(invec), if(mapisdefined(occurrences, invec[i]), my(pp = mapget(occurrences, invec[i])); outvec[i] = outvec[pp] , mapput(occurrences, invec[i], i); outvec[i] = u; u++ )); outvec; };

write_to_bfile(start_offset, vec, bfilename) = { for(n=1, length(vec), write(bfilename, (n+start_offset)-1, " ", vec[n])); }

A000010(n) = eulerphi(n);

write_to_bfile(1, rgs_transform(vector(10000, n, A000010(n))), "b286610.txt");

CROSSREFS

Cf. A000010, A210719 (positions of records, and also the first occurrence of each n).

Cf. also A101296, A286603, A286605, A286619, A286621, A286622, A286626, A286378 for similarly constructed sequences.

Sequence in context: A062821 A296080 A180633 * A304117 A326790 A232479

Adjacent sequences:  A286607 A286608 A286609 * A286611 A286612 A286613

KEYWORD

nonn

AUTHOR

Antti Karttunen, May 11 2017

STATUS

approved

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Last modified January 23 13:33 EST 2020. Contains 331171 sequences. (Running on oeis4.)