OFFSET
1,2
EXAMPLE
21 is in the sequence since uphi(21) = 12 = uphi(23) - uphi(22) = 22 - 10.
MATHEMATICA
uphi[n_] := If[n>1, (Times @@ (Table[ #[[1]]^ #[[2]] - 1, {1} ] & /@ FactorInteger[n]))[[1]], 1]; Select[Range[10^7], uphi[#] == uphi[# + 2] - uphi[# + 1] &]
PROG
(PARI) uphi(n) = my(f=factor(n)); prod(i=1, #f~, f[i, 1]^f[1, 2]-1);
isok(n) = uphi(n) == uphi(n+2) - uphi(n+1); \\ Michel Marcus, Jan 26 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Jan 26 2018
EXTENSIONS
a(7)-a(26) from Giovanni Resta, Jan 26 2018
STATUS
approved