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A048129 Becomes prime or 4 after exactly 7 iterations of f(x) = sum of prime factors of x. 1
393, 422, 614, 674, 692, 886, 889, 934, 993, 1006, 1270, 1285, 1502, 1522, 1524, 1542, 1726, 1822, 2018, 2217, 2326, 2386, 2402, 2474, 2545, 2654, 2733, 2734, 2761, 2858, 2876, 3005, 3022, 3039, 3054, 3147, 3193, 3261, 3453, 3507, 3512, 3518, 3589 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
f(x) = sum of prime factors with multiplicity, so that f(1500) = 2+2+3+5+5+5 = 22.
LINKS
MATHEMATICA
spf[n_]:=Total[Flatten[Table[#[[1]], {#[[2]]}]&/@FactorInteger[n]]]; pf7Q[ n_]:= Module[ {lst=NestList[spf, n, 7]}, NoneTrue[Most[lst], PrimeQ] && !MemberQ[Most[lst], 4]&&(PrimeQ[Last[lst]]||Last[lst]==4)]; Select[Range[ 3600], pf7Q] (* Harvey P. Dale, Jul 11 2014 *)
CROSSREFS
Sequence in context: A068288 A085019 A105233 * A045194 A105210 A256742
KEYWORD
nonn
AUTHOR
STATUS
approved

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Last modified March 28 16:34 EDT 2024. Contains 371254 sequences. (Running on oeis4.)