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 A307961 The number of coreful perfect numbers (A307958) below 10^n. 2
 0, 1, 9, 94, 940, 9359, 93611, 936098, 9361056, 93610484 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Table of n, a(n) for n=1..10. FORMULA a(n) ~ c * 10^n, were c = 0.009361... is the asymptotic density of the coreful perfect numbers (A307960). MATHEMATICA f[p_, e_] := (p^(e+1)-1)/(p-1)-1; csigma[1]=1; csigma[n_] := Times @@ (f @@@ FactorInteger[n]); cpQ[n_] := csigma[n] == 2*n; s={}; c=0; p=100; Do[If[k==p, AppendTo[s, c]; p*=10]; If[cpQ[k], c++], {k, 1, 1000001}]; s CROSSREFS Cf. A307822, A307958, A307960. Sequence in context: A231658 A034992 A048359 * A099297 A057782 A115071 Adjacent sequences: A307958 A307959 A307960 * A307962 A307963 A307964 KEYWORD nonn,more AUTHOR Amiram Eldar, May 08 2019 STATUS approved

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Last modified August 6 03:16 EDT 2024. Contains 374957 sequences. (Running on oeis4.)