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A064802 a(n) = Min { m > n | prime factorizations of m and n differ in one factor only}, a(1) = 1. 3
1, 3, 5, 6, 7, 9, 11, 12, 15, 14, 13, 18, 17, 21, 21, 24, 19, 27, 23, 28, 33, 26, 29, 36, 35, 34, 45, 42, 31, 42, 37, 48, 39, 38, 49, 54, 41, 46, 51, 56, 43, 63, 47, 52, 63, 58, 53, 72, 77, 70, 57, 68, 59, 81, 65, 84, 69, 62, 61, 84, 67, 74, 99, 96, 85, 78, 71, 76, 87, 98, 73 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(A000040(k)) = A000040(k + 1).

A094457 gives next smaller comparable number, replacing the prime factor 2 with 1. - Michael De Vlieger, Jan 31 2015

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

EXAMPLE

20 = 2 * 2 * 5: as 2 * 3 * 5 > 2 * 2 * 7 = 28 we have a(20) = 28.

MATHEMATICA

f[n_] := Block[{g}, g[x_] := Flatten[Table[#1, {#2}] & @@@ FactorInteger@ x]; If[n == 1, 1, Min[Times @@ MapAt[NextPrime, g[n], #] & /@ Range[Length@ g[n]]]]]; Array[f, 71] (* Michael De Vlieger, Jan 31 2015 *)

CROSSREFS

Cf. A000040, A094457.

Sequence in context: A284852 A285627 A320472 * A233570 A181766 A047584

Adjacent sequences:  A064799 A064800 A064801 * A064803 A064804 A064805

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Oct 21 2001

STATUS

approved

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Last modified September 21 17:46 EDT 2019. Contains 327273 sequences. (Running on oeis4.)