A333101 Numbers k such that both k and k + 2 are noncototients (A005278).

50, 170, 266, 290, 344, 518, 532, 534, 650, 686, 722, 730, 872, 962, 1036, 1158, 1166, 1332, 1394, 1462, 1464, 1586, 1634, 1682, 1804, 1864, 1922, 1946, 1970, 2034, 2072, 2074, 2116, 2134, 2262, 2314, 2316, 2318, 2330, 2420, 2534, 2598, 2666, 2668, 2772, 2822

Offset

1,1

Links

Table of n, a(n) for n=1..46.

Eric Weisstein's World of Mathematics, Noncototient.

Wikipedia, Noncototient.

Example

50 is a term since both 50 and 52 are noncototients.

Mathematica

nmax = 3000; cototientQ[n_?EvenQ] := (x = n; While[test = x - EulerPhi[x] == n ; Not[test || x > 2*nmax], x++]; test); cototientQ[n_?OddQ] = True; nonc = Select[Range[nmax], !cototientQ[#]&]; nonc[[Flatten[Position[Differences[nonc], 2]]]] (* after Jean-François Alcover at A005278 *)

Crossrefs

Cf. A005278, A072296, A231964, A306952, A333100.

Sequence in context: A085445 A048511 A206128 * A206121 A349808 A244696

Adjacent sequences: A333098 A333099 A333100 * A333102 A333103 A333104

Keyword

nonn

Author

Amiram Eldar, Mar 07 2020

Status

approved