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A298761
Numbers n such that n = pi(n) + uphi(n), where pi = A000720, uphi = A047994.
0
2, 20, 35, 40, 44, 215, 235, 245, 2611, 23319, 26288, 65113, 174647, 318544, 1301317, 1302509, 1919376, 3719225, 5021647, 10885081, 36319939, 49172608, 70112131, 70113559, 325575773, 514258883, 742327529, 1069238453
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