A171815 Values of A171743 that are 1 less than a prime, listed in the order in which they appear.
4, 4, 4, 6, 12, 12, 16, 40, 72, 60, 60, 72, 72, 88, 96, 96, 96, 180, 232, 192, 180, 192, 192, 352, 192, 280, 432, 240, 240, 420, 240, 408, 336, 432, 352, 592, 600, 408, 336, 640, 616, 456, 448, 576, 432, 672, 432, 400, 432, 448, 600, 928, 576, 672, 928, 672, 1008
Offset: 1
Programs
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Mathematica
Do[a=EulerPhi[Prime[n] + Prime[n+1]];If[PrimeQ[a+1],Print[a]],{n,2^10}] (* Metin Sariyar, Nov 24 2019 *) Select[EulerPhi[Total[#]]&/@Partition[Prime[Range[200]],2,1],PrimeQ[#+1]&] (* Harvey P. Dale, Dec 25 2022 *)
Extensions
a(14) corrected and terms beyond a(14) appended by R. J. Mathar, Jan 30 2010
Named edited by Michel Marcus, Nov 24 2019