A330871 Numbers k such that k and k+1 are both phi-practical numbers (A260653).

1, 2, 3, 15, 255, 735, 2624, 3135, 4095, 4784, 5264, 5984, 7215, 7424, 7904, 9344, 10064, 10335, 10815, 11024, 11984, 12375, 12495, 13695, 16184, 16575, 22575, 22784, 22815, 26144, 26264, 27104, 30015, 30855, 30975, 32384, 33824, 34335, 34544, 38024, 38415, 39104

Offset: 1

Author

Amiram Eldar, Apr 29 2020

Keywords

• nonn

Examples

			1 is a term since both 1 and 2 are phi-practical numbers.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A260653, A287681.

Programs

Mathematica

phiPracticalQ[n_] := If[n<1, False, If[n==1, True, (lst = Sort @ EulerPhi @ Divisors[n]; ok=True; Do[If[lst[[m]]>Sum[lst[[l]], {l, 1, m-1}]+1, (ok=False; Break[])], {m, 1, Length[lst]}]; ok)]]; Select[Range[40000], phiPracticalQ[#] && phiPracticalQ[#+1] &] (* after Frank M Jackson at A260653 *)