A079431 - OEIS

A079431

Least m>n with same smallest odd prime factor as n.

2, 4, 6, 8, 10, 9, 14, 16, 12, 20, 22, 15, 26, 28, 18, 32, 34, 21, 38, 25, 24, 44, 46, 27, 35, 52, 30, 49, 58, 33, 62, 64, 36, 68, 40, 39, 74, 76, 42, 50, 82, 45, 86, 88, 48, 92, 94, 51, 56, 55, 54, 104, 106, 57, 65, 77, 60, 116, 118, 63, 122, 124, 66, 128, 70, 69, 134, 136

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OFFSET

1,1

COMMENTS

A078701(a(n))=A078701(n), A078701(i)<>A078701(n), n<i<a(n);

n + A078701(n) <= a(n) <= 2*n;

a(2^k) = 2^(k+1), as A078701(2^k) = 1.

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

N:= 100:

A:= Vector(N):

p:= 2:

p:= nextprime(p);

if p > N then break fi;

R:= select(k -> A[k] = 0, [$1..N]);

S:= select(`<=`, R, N/p);

A[p*S]:= Vector(p*R[2..1+nops(S)]);

od:

for k from 0 to ilog2(N) do A[2^k]:= 2^(k+1) od:

convert(A, list); # Robert Israel, Oct 25 2017

MATHEMATICA

sopf[n_] := SelectFirst[FactorInteger[n][[All, 1]], # > 2&];

a[n_] := For[p = sopf[n]; m = n+1, True, m++, If[p == sopf[m], Return[m]]];

Array[a, 100] (* Jean-François Alcover, Mar 09 2019 *)

CROSSREFS

Cf. A079432(n) = a(a(n)).

Cf. A078701.

Sequence in context: A319806 A055952 A061243 * A081472 A097660 A238898

Adjacent sequences: A079428 A079429 A079430 * A079432 A079433 A079434

KEYWORD

nonn,look

AUTHOR

Reinhard Zumkeller, Jan 09 2003

STATUS

approved