A100392 - OEIS

A100392

Numbers k such that A006530(k-1) < A006530(k) > A006530(k+1).

3, 5, 7, 11, 13, 17, 19, 23, 26, 29, 31, 34, 37, 41, 43, 47, 49, 51, 53, 55, 59, 61, 65, 67, 69, 71, 73, 76, 79, 83, 86, 89, 94, 97, 99, 101, 103, 107, 109, 111, 113, 116, 118, 122, 127, 129, 131, 134, 137, 139, 142, 146, 149, 151, 155, 157, 161, 163, 167, 173, 179

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OFFSET

1,1

COMMENTS

A006530(k) is the largest prime factor of k.

The sequence contains all odd primes.

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = A082417(n) + 1. - T. D. Noe, Nov 26 2007

EXAMPLE

26 is here because the largest prime factors of 25, 26, 27 are 5, 13, 3.

MATHEMATICA

<<NumberTheory`NumberTheoryFunctions` mxp[x_] :=Max[PrimeFactorList[x]]; ta={{0}}; Do[s1=mxp[n-1]; s=mxp[n]; s2=mxp[n+1]; If[Greater[s, s1]&&Greater[s, s2], Print[{n, {s1, s, s2}}]; ta=Append[ta, n]], {n, 1, 1000}]ta=Delete[ta, 1]

With[{lpfs=Table[FactorInteger[n][[-1, 1]], {n, 200}]}, Flatten[Position[ Partition[ lpfs, 3, 1], _?(First[#]<#[[2]]>Last[#]&), {1}, Heads-> False]]+ 1] (* Harvey P. Dale, Feb 22 2014 *)

CROSSREFS

Cf. A006530, A100390, A100393.

Sequence in context: A332075 A122089 A109860 * A309203 A176847 A067019

Adjacent sequences: A100389 A100390 A100391 * A100393 A100394 A100395

KEYWORD

nonn

AUTHOR

Labos Elemer, Dec 14 2004

EXTENSIONS

Edited by Don Reble, Jun 13 2007

STATUS

approved