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
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Dec 10 2001
STATUS
approved