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URL: https://oeis.org/A388001

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A388001
Numbers k such that sigma(k) = psi(k) + phi(k) + tau(k).
12
80, 608, 16830, 149984, 216568, 251392, 534114, 1329174, 2135104, 4087864, 47959496, 70884608, 227556608, 974754272, 2154622208, 4210790624, 34963314688, 42710603776, 63839574016
OFFSET
1,1
COMMENTS
a(20), if it exists, is greater than 10^11. - Lyle Blosser, Jan 23 2026
EXAMPLE
80 is in the sequence since sigma(80) = 186 = 144 + 32 + 10 = psi(80) + phi(80) + tau(80).
MATHEMATICA
f1[p_, e_] := (p^(e + 1) - 1)/(p - 1);
f2[p_, e_] := (p + 1)*p^(e - 1);
f3[p_, e_] := (p - 1)*p^(e - 1);
f4[p_, e_] := e + 1;
q[k_] := Module[{f = FactorInteger[k]}, Times @@ f1 @@@ f == Times @@ f2 @@@ f + Times @@ f3 @@@ f + Times @@ f4 @@@ f]; Select[Range[2, 6*10^5], q] (* Amiram Eldar, Oct 14 2025 *)
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
S. I. Dimitrov, Oct 14 2025
EXTENSIONS
a(11)-a(14) from Lyle Blosser, Jan 19 2026
a(15)-a(19) from Lyle Blosser, Jan 23 2026
STATUS
approved