A327163 - OEIS

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A327163

Lexicographically earliest sequence such that for all i, j, a(i) = a(j) => f(i) = f(j), where f(n) = gcd(n,usigma(n)) * (-1)^[gcd(n,usigma(n))==n], and usigma is the sum of unitary divisors of n (A034448).

1, 2, 2, 2, 2, 3, 2, 2, 2, 4, 2, 5, 2, 4, 6, 2, 2, 7, 2, 8, 2, 4, 2, 9, 2, 4, 2, 5, 2, 7, 2, 2, 6, 4, 2, 4, 2, 4, 2, 4, 2, 7, 2, 5, 10, 4, 2, 5, 2, 4, 6, 4, 2, 7, 2, 11, 2, 4, 2, 12, 2, 4, 2, 2, 2, 7, 2, 4, 6, 4, 2, 13, 2, 4, 2, 5, 2, 7, 2, 4, 2, 4, 2, 5, 2, 4, 6, 5, 2, 14, 15, 5, 2, 4, 16, 9, 2, 4, 6, 8, 2, 7, 2, 4, 6

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OFFSET

1,2

COMMENTS

Restricted growth sequence transform of function f, defined as f(n) = -A323166(n) = -n when n is one of unitary multiply-perfect numbers (A327158), otherwise f(n) = A323166(n) = gcd(n,A034448(n))

For all i, j:

A305800(i) = A305800(j) => a(i) = a(j) => A327164(i) = A327164(j).

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..87360

PROG

(PARI)

up_to = 87360;

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

A034448(n) = { my(f=factorint(n)); prod(k=1, #f~, 1+(f[k, 1]^f[k, 2])); }; \\ After code in A034448

A323166(n) = gcd(n, A034448(n));

Aux327163(n) = { my(u=A323166(n)); u*((-1)^(u==n)); };

v327163 = rgs_transform(vector(up_to, n, Aux327163(n)));

A327163(n) = v327163[n];

CROSSREFS

Cf. A034448, A305800, A323166, A327158, A327164.

Cf. also A326193.

Sequence in context: A320018 A327162 A326193 * A324538 A305976 A074592

Adjacent sequences: A327160 A327161 A327162 * A327164 A327165 A327166

KEYWORD

nonn

AUTHOR

Antti Karttunen, Aug 28 2019

STATUS

approved