A279183 -id:A279183 - cp's OEIS frontend

A279011 Numbers k such that phi(6k) is either phi(6k-2) or phi(6k+2), where phi is Euler's totient function A000010.

1, 2, 12, 152, 222, 268, 362, 432, 723, 992, 1517, 2532, 2567, 8472, 9718, 9858, 13498, 15738, 34732, 35898, 44092, 60363, 69312, 75168, 75973, 82752, 87208, 88888, 98198, 105852, 114392, 126848, 128672, 135368, 141093, 161268, 221223, 233788, 301513, 328358

Offset: 1

N. J. A. Sloane, Dec 10 2016

nonn

Amiram Eldar, Table of n, a(n) for n = 1..1554
Dov Jarden, Recurring Sequences, Riveon Lematematika, Jerusalem, 1966. [Annotated scanned copy] See p. 67.

Cf. A000010.

Union of A279183 and A279184.

[n: n in [1..1000000] | not (EulerPhi(6*n) eq EulerPhi(6*n-2)) eq (EulerPhi(6*n) eq EulerPhi(6*n+2))]; // Vincenzo Librandi, Dec 12 2016

Select[Range[10^6], Function[k, Or @@ Map[EulerPhi[6 k] == EulerPhi@ # &, 6 k + {-2, 2}]]] (* Michael De Vlieger, Dec 12 2016 *)
Select[Range[330000],EulerPhi[6#]==EulerPhi[6#-2]||EulerPhi[6#]==EulerPhi[6#+2]&] (* Harvey P. Dale, Jul 07 2025 *)

More terms from Vincenzo Librandi, Dec 12 2016

A279184 Numbers k such that phi(6k) = phi(6k+2), where phi is Euler's totient function A000010.

Original entry on oeis.org

268, 723, 9718, 9858, 13498, 15738, 35898, 60363, 75168, 75973, 87208, 88888, 98198, 126848, 135368, 141093, 161268, 221223, 233788, 301513, 328358, 330633, 419148, 507648, 527928, 543468, 551238, 556418, 586018, 725958, 772508, 964588, 985728

Offset: 1

N. J. A. Sloane, Dec 10 2016

nonn

Amiram Eldar, Table of n, a(n) for n = 1..794
Dov Jarden, Recurring Sequences, Riveon Lematematika, Jerusalem, 1966. [Annotated scanned copy] See p. 67.

Cf. A000010.

A279011 is the union of A279183 and A279184.

[n: n in [1..2*10^6] | EulerPhi(6*n) eq EulerPhi(6*n+2)]; // Vincenzo Librandi, Dec 11 2016

select( k -> numtheory:-phi(6*k)=numtheory:-phi(6*k+2), [$1..10^6]); # Robert Israel, Dec 11 2016

a = {}; Do[If[EulerPhi[6 k] == EulerPhi[6 k + 2], AppendTo[a, k]], {k, 1000000}]; a (* Vincenzo Librandi, Dec 11 2016 *)

isok(k) = eulerphi(6*k) == eulerphi(6*k+2); \\ Michel Marcus, Dec 11 2016

a(8)-a(33) from Robert Israel, Dec 11 2016

cp's OEIS Frontend

A279011 Numbers k such that phi(6k) is either phi(6k-2) or phi(6k+2), where phi is Euler's totient function A000010.

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