A046427 Numbers requiring 7 steps to reach a prime under the prime factor concatenation procedure.

91, 128, 196, 305, 344, 416, 438, 456, 554, 656, 690, 707, 746, 750, 779, 897, 910, 950, 1014, 1060, 1098, 1122, 1199, 1209, 1247, 1380, 1507, 1545, 1606, 1679, 1680, 1700, 1711, 1769, 1833, 1884, 1887, 1888, 1928, 1971, 1984, 2000, 2169, 2176, 2192, 2198

Offset

1,1

Links

Table of n, a(n) for n=1..46.

Patrick De Geest, Home Primes

Mathematica

numberSteps[x_]:=Module[{n, steps, digits, i}, n=x; steps=0; While[ !PrimeQ[n]&&steps<10, factors=FactorInteger[n]; digits={}; For[i=1, i<=Length[factors], i++, digits=Join[digits, Flatten[ Table[IntegerDigits[factors[[i, 1]]], {factors[[i, 2]]}]]]; ]; n=FromDigits[digits]; steps++; ]; Return[steps]]; For[i=1, i<2000, i++, If[numberSteps[i]==7, Print[i]; ]; ]; (* Sam Handler (sam_5_5_5_0(AT)yahoo.com), Aug 16 2006 *)

Crossrefs

Cf. A037271, A046411.

Sequence in context: A351336 A328662 A020235 * A179338 A020238 A220171

Adjacent sequences: A046424 A046425 A046426 * A046428 A046429 A046430

Keyword

nonn,base

Author

Patrick De Geest, Jun 15 1998

Extensions

More terms from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Aug 16 2006

Extended and edited by Charles R Greathouse IV, Apr 28 2010

Status

approved