A173979 - OEIS

A173979

a(n) is the smallest number m from A173977 for which A020639(2m-1) = prime(n).

5, 13, 25, 127, 85, 196, 181, 472, 421, 946, 685, 1210, 925, 1105, 1882, 3157, 1861, 2446, 2521, 3541, 4306, 4690, 3961, 6160, 5707, 5305, 5725, 6922, 9436, 8065, 8581, 10207, 9661, 13336, 12307, 12796, 14752, 18955, 14965

(list; graph; refs; listen; history; text; internal format)

OFFSET

2,1

COMMENTS

If the requirement that m be an element of A173977 is dropped, the sequence becomes A006254. - R. J. Mathar, Nov 02 2011

LINKS

Amiram Eldar, Table of n, a(n) for n = 2..1000

MAPLE

A020639 := proc(n) if n = 1 then 1; else min(op(numtheory[factorset](n)) ) ; end if; end proc:

isA173977 := proc(n) A020639(2*n-1) < A020639(2*n-3) ; end proc:

A173979 := proc(n) local p, m ; p := ithprime(n) ; for m from 1 do if A020639(2*m-1) = p and isA173977(m) then return m ; end if; end do: end proc:

seq(A173979(n), n=2..40) ; # R. J. Mathar, Sep 02 2011

MATHEMATICA

lpf[n_] := lpf[n] = FactorInteger[n][[1, 1]]; q[n_] := lpf[2*n-1] < lpf[2*n-3]; seq[len_] := Module[{s = Table[0, {Prime[len+1]}], k = 2, c = 0, p}, While[c < len, If[q[k], p = lpf[2*k-1]; If[p <= Length[s] && s[[p]] == 0, c++; s[[p]] = k]]; k++]; Select[s, # > 0 &]]; seq[100] (* Amiram Eldar, Oct 25 2024 *)

CROSSREFS

Cf. A006254, A020639, A173977.

Sequence in context: A018394 A309383 A147451 * A190446 A188471 A139595

Adjacent sequences: A173976 A173977 A173978 * A173980 A173981 A173982

KEYWORD

nonn,changed

AUTHOR

Vladimir Shevelev, Mar 04 2010

EXTENSIONS

Name corrected by Vladimir Shevelev, Mar 15 2010

STATUS

approved