|
| |
|
|
A006601
|
|
Numbers n such that n, n+1, n+2 and n+3 have the same number of divisors.
(Formerly M5420)
|
|
10
| |
|
|
242, 3655, 4503, 5943, 6853, 7256, 8392, 9367, 10983, 11605, 11606, 12565, 12855, 12856, 12872, 13255, 13782, 13783, 14312, 16133, 17095, 18469, 19045, 19142, 19143, 19940, 20165, 20965, 21368, 21494, 21495, 21512, 22855, 23989, 26885
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,1
|
|
|
REFERENCES
| M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 840.
J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 242, p. 67, Ellipses, Paris 2008.
R. K. Guy, Unsolved Problems in Number Theory, B18.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
|
|
|
LINKS
| T. D. Noe, Table of n, a(n) for n=1..1000
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].
|
|
|
MATHEMATICA
| f[n_]:=Length[Divisors[n]]; lst={}; Do[If[f[n]==f[n+1]==f[n+2]==f[n+3], AppendTo[lst, n]], {n, 8!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Dec 14 2009]
dsQ[n_]:=Length[Union[DivisorSigma[0, Range[n, n+3]]]]==1; Select[Range[ 30000], dsQ] (* From Harvey P. Dale, Nov 23 2011 *)
|
|
|
CROSSREFS
| Cf. A000005, A005237, A005238.
Sequence in context: A070284 A160551 A165935 * A035748 A022153 A194788
Adjacent sequences: A006598 A006599 A006600 * A006602 A006603 A006604
|
|
|
KEYWORD
| nonn,easy,nice
|
|
|
AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
|
|
|
EXTENSIONS
| More terms from Olivier Gerard (olivier.gerard(AT)gmail.com)
|
| |
|
|
