A065986 Numbers n such that Sigma(n) = EulerPhi(n+1) + EulerPhi(n) + EulerPhi(n-1).

6, 147, 286, 376, 534, 738, 805, 2392, 2406, 4324, 8214, 9606, 10362, 12126, 16263, 17511, 27639, 29151, 39215, 48616, 60687, 61132, 61915, 141526, 142610, 147890, 153530, 160748, 189501, 212134, 221121, 253022, 324650, 326691, 368296, 404716, 453699

Offset

1,1

Links

Jon E. Schoenfield, Table of n, a(n) for n = 1..80 (first 60 terms from Harry J. Smith)

Example

Sigma(6) = 12 = 6 + 2 + 4 = EulerPhi(7) + EulerPhi(6) + EulerPhi(5).

Mathematica

Select[Range@500000, EulerPhi@(# + 1) + EulerPhi@(#) + EulerPhi@(# - 1) == DivisorSigma[1, #] &] (* Vincenzo Librandi, Jun 17 2018 *)

Prog

(PARI) { n=e1=e2=0; for (m=2, 10^9, e2=e1; e1=e; e=eulerphi(m+1); if (sigma(m) == e + e1 + e2, write("b065986.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Nov 05 2009
(Magma) [n: n in [2..10^6] | EulerPhi(n+1)+EulerPhi(n)+ EulerPhi(n-1) eq SumOfDivisors(n)]; // Vincenzo Librandi, Jun 17 2018

Crossrefs

Cf. A000010.

Sequence in context: A250389 A358800 A063419 * A199226 A012791 A347842

Adjacent sequences: A065983 A065984 A065985 * A065987 A065988 A065989

Keyword

nonn

Author

Joseph L. Pe, Dec 10 2001

Status

approved