

A159560


Minimal recursive sequence beginning with 3 such that A001221(a(n)) = A001221(n).


11



3, 4, 5, 7, 10, 11, 13, 16, 18, 19, 20, 23, 24, 26, 27, 29, 33, 37, 38, 39, 40, 41, 44, 47, 48, 49, 50, 53, 60, 61, 64, 65, 68, 69, 72, 73, 74, 75, 76, 79, 84, 89, 91, 92, 93, 97, 98, 101, 104, 106, 108, 109, 111, 112, 115, 116, 117, 121, 126, 127, 129, 133, 137, 141, 150
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OFFSET

2,1


LINKS

Amiram Eldar, Table of n, a(n) for n = 2..10000
V. Shevelev, Several results on sequences which are similar to the positive integers, arXiv:0904.2101 [math.NT], 2009.


FORMULA

a(n+1) = min{m > a(n): A001221(m) = A001221(n+1)}.


MAPLE

A001221 := proc(n) nops(numtheory[factorset](n)) ; end proc:
A159560 := proc(n) option remember; if n = 2 then 3; else for a from procname(n1)+1 do if A001221(a) = A001221(n) then return a; end if; end do: end if; end proc:
seq(A159560(n), n=2..70) ; # R. J. Mathar, Oct 30 2010


MATHEMATICA

a[2] = 3; a[n_] := a[n] = For[an = a[n  1] + 1, True, an++, If[PrimeNu[an] == PrimeNu[n], Return[an]]];
Table[a[n], {n, 2, 66}] (* JeanFrançois Alcover, Nov 14 2017 *)


CROSSREFS

Cf. A001221, A159559.
Sequence in context: A047365 A353448 A048342 * A288427 A030502 A201025
Adjacent sequences: A159557 A159558 A159559 * A159561 A159562 A159563


KEYWORD

nonn


AUTHOR

Vladimir Shevelev, Apr 15 2009


EXTENSIONS

Corrected (4 inserted, 8 removed) and extended beyond 53 by R. J. Mathar, Oct 30 2010


STATUS

approved



