login
A047824
Becomes prime after exactly 5 iterations of f(x) = sum of prime factors of x.
0
134, 177, 262, 268, 398, 422, 466, 524, 531, 536, 573, 614, 669, 706, 742, 753, 796, 817, 818, 844, 849, 898, 915, 921, 932, 933, 934, 974, 1006, 1048, 1072, 1149, 1165, 1202, 1222, 1227, 1228, 1238, 1239, 1243, 1294, 1322, 1347, 1354, 1385, 1393, 1398
OFFSET
1,1
COMMENTS
f(x) = sum of prime factors without multiplicity, so that f(1500) = 2+3+5 = 10.
MATHEMATICA
p5iQ[n_]:=PrimeQ[NestList[Total[Transpose[FactorInteger[#]][[1]]]&, n, 5]] == {False, False, False, False, False, True}; Select[Range[2000], p5iQ] (* Harvey P. Dale, May 21 2015 *)
CROSSREFS
Sequence in context: A252133 A255795 A048128 * A020353 A050963 A051387
KEYWORD
nonn
STATUS
approved