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A065391 Numbers n such that A062401(n) = phi(sigma(n)) is increasing; i.e., A062401(n) represents a new peak, so that A062401(n) > A062401(k) for all k < n. 3
1, 2, 4, 8, 9, 16, 32, 36, 64, 100, 144, 256, 324, 400, 576, 900, 1296, 1600, 2304, 2916, 3600, 5184, 8100, 9216, 11664, 14400, 20736, 22500, 25600, 30276, 32400, 41616, 46656, 57600, 69696, 72900, 82944, 90000, 104976, 115600, 121104, 129600 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Indices of records in A062401. - Michael De Vlieger, Dec 06 2018

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..100

EXAMPLE

Initial segment of A062401: {1,2,2,6,2,4,4,8,12,6,4,12,6,8,8,30,6,...}. Peak values [those exceeding all previous ones] are 1,2,6,8,12,30 reached at positions 1,2,4,8,9,16, respectively. Entries > 2 are exact powers and except 2, 8 and 32 seem to be squares.

MATHEMATICA

a = 0; s = 0; Do[s = EulerPhi[DivisorSigma[1, n]]; If[s > a, a = s; Print[n]], {n, 1, 10^6}]

(* Second program: *)

With[{s = Array[EulerPhi@ DivisorSigma[1, #] &, 2*10^5]}, Map[FirstPosition[s, #][[1]] &, Union@ FoldList[Max, s]]] (* Michael De Vlieger, Dec 06 2018 *)

PROG

(PARI) { n=r=0; for (m=1, 10^9, x=eulerphi(sigma(m)); if (x > r, r=x; write("b065391.txt", n++, " ", m); if (n==100, return)) ) } \\ Harry J. Smith, Oct 18 2009

CROSSREFS

Cf. A000010, A000203, A062401, A062402, A065392.

Sequence in context: A046680 A331992 A113570 * A161792 A111261 A276773

Adjacent sequences:  A065388 A065389 A065390 * A065392 A065393 A065394

KEYWORD

nonn

AUTHOR

Labos Elemer, Nov 05 2001

STATUS

approved

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Last modified June 22 09:57 EDT 2021. Contains 345375 sequences. (Running on oeis4.)