OFFSET
1,1
COMMENTS
The unitary version of A037170.
EXAMPLE
20 is in the sequence since pi(20) + uphi(20) = 8 + 12 = 20.
MATHEMATICA
uphi[n_] := (Times @@ (Table[#[[1]]^#[[2]] - 1, {1}] & /@ FactorInteger[n]))[[1]]; seqQ[n_] := (n - uphi[n] == PrimePi[n]); Select[Range[10^7], seqQ]
PROG
(PARI) uphi(n) = my(f=factor(n)); prod(k=1, #f~, f[k, 1]^f[k, 2]-1);
isok(n) = n == primepi(n) + uphi(n); \\ Michel Marcus, Feb 13 2018
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Jan 26 2018
EXTENSIONS
a(20)-a(22) from Daniel Suteu, Mar 28 2018
a(23)-a(28) from Daniel Suteu, Nov 18 2018
STATUS
approved