A373528 Odd numbers k such that k, k+2 and k+4 all have at least two divisors with the same value of the Euler totient function (A000010).

4142435, 26196331, 77118741, 89690821, 102974571, 196054673, 201060275, 206568171, 277322153, 280039833, 401784953, 402492695, 415097613, 437290371, 515636303, 526721895, 534746581, 549806211, 575090395, 580329603, 625833871, 629588043, 702183625, 710983971, 716133481

Offset

1,1

Comments

Numbers k such that k, k+2 and k+4 are all in A359563.

Links

Amiram Eldar, Table of n, a(n) for n = 1..100

Mathematica

q[n_] := !UnsameQ @@ EulerPhi[Divisors[n]]; seq[kmax_] := Module[{tri = q /@ {1, 3, 5}, s = {}, k = 7}, While[k < kmax, If[And @@ tri, AppendTo[s, k - 6]]; tri = Join[Rest[tri], {q[k]}]; k+=2]; s]; seq[3*10^7]

Prog

(PARI) is(k) = k>1 && k%2 && numdiv(k) > #Set(apply(x->eulerphi(x), divisors(k)));
lista(kmax) = {my(q1 = 0, q2 = 0, q3); forstep(k = 5, kmax, 2, q3 = is(k); if(q1 && q2 && q3, print1(k-4, ", ")); q1 = q2; q2 = q3); }

Crossrefs

Subsequence of A359563 and A373527.

Cf. A000010, A102190.

Sequence in context: A333376 A230755 A204151 * A205245 A366507 A237174

Adjacent sequences: A373525 A373526 A373527 * A373529 A373530 A373531

Keyword

nonn

Author

Amiram Eldar, Jun 08 2024

Status

approved