The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A286289 Least number to start a run of exactly n nondecreasing values of the Euler phi function (A000010). 3
 314, 6, 315, 14, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(6) > 10^7. - Michael De Vlieger, May 19 2017 a(6) > 10^13. - Giovanni Resta, Nov 12 2019 REFERENCES M. F. Hasler, Posting to Sequence Fans Mailing List, May 06 2017 LINKS EXAMPLE From Michael De Vlieger, May 19 2017: (Start) A run of subsequent numbers with nondecreasing phi is of length 1 if it consists of a single number n with phi(n-1) > phi(n) > phi(n+1) (else n belongs to a run of length >= 2). This happens first for a(1) = 314. Phi(14..18) = (6, 8, 8, 16, 6), therefore the first run of 4 numbers with nondecreasing phi(= A000010) starts at a(4) = 14. (End) MATHEMATICA Prepend[#, Module[{k = 2}, While[Sign@ Differences@ EulerPhi[k + {-1, 0, 1}] != {-1, -1}, k++]; k]] &@ Function[s, Function[r, If[Length@ # > 0, #[[1, 1]], -1] &@ Select[s, Length@ # == r &]] /@ Range@ Max@ Map[Length, s]]@ DeleteCases[SplitBy[MapIndexed[Function[k, (2 Boole[#1 <= #2] - 1) k & @@ #1]@ First@ #2 &, Partition[Array[EulerPhi, 10^7], 2, 1]], Sign], w_ /; First@ w < 0] (* Michael De Vlieger, May 19 2017 *) CROSSREFS Cf. A000010, A284597, A285893, A286287, A286288. Sequence in context: A164772 A068650 A106156 * A219961 A107116 A107115 Adjacent sequences: A286286 A286287 A286288 * A286290 A286291 A286292 KEYWORD nonn,more AUTHOR N. J. A. Sloane, May 16 2017 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 2 10:56 EST 2022. Contains 358493 sequences. (Running on oeis4.)