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A067249 Digits of sigma(n) end in phi(n). 1

%I

%S 1,6,84,112,141,294,1188,1320,2508,4584,5406,8850,14270,17416,23320,

%T 31152,79035,117576,125576,132066,149877,160664,162514,164024,167970,

%U 170980,177744,184584,223286,1119636,1124592,1216644,1481800,1566920,1626716

%N Digits of sigma(n) end in phi(n).

%C There are only 46 terms up to 10 million. - _Harvey P. Dale_, Oct 04 2012

%H Harvey P. Dale and Donovan Johnson, <a href="/A067249/b067249.txt">Table of n, a(n) for n = 1..150</a> (first 46 terms from Harvey P. Dale)

%e sigma(79035) = 138240 ends in phi(79035) = 38240, so 79035 is a term of the sequence.

%t (*returns true if a ends with b, false o.w.*) f[a_, b_] := Module[{c, d, e, g, h, i, r}, r = False; c = ToString[a]; d = ToString[b]; e = StringLength[c]; g = StringPosition[c, d]; h = Length[g]; If[h > 0, i = g[[h]]; If[i[[2]] == e, r = True]]; r]; Select[Range[10^5], f[DivisorSigma[1, # ], EulerPhi[ # ]] & ]

%t dsepQ[n_]:=Module[{ep=EulerPhi[n]},Mod[DivisorSigma[1,n],10^ IntegerLength[ ep]]==ep]; Select[Range[250000],dsepQ] (* _Harvey P. Dale_, Oct 04 2012 *)

%K base,nonn

%O 1,2

%A _Joseph L. Pe_, Feb 20 2002

%E More terms from _Vladeta Jovovic_, Feb 22 2002

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Last modified December 12 09:36 EST 2019. Contains 329953 sequences. (Running on oeis4.)