The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A215113

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A215113

a(n) is the number of different prime divisors of A214723(n).
(history; published version)

#14 by Bruno Berselli at Wed May 17 03:17:38 EDT 2017

STATUS

proposed

approved

#13 by G. C. Greubel at Tue May 16 21:55:43 EDT 2017

STATUS

editing

proposed

#12 by G. C. Greubel at Tue May 16 21:55:33 EDT 2017

LINKS

G. C. Greubel, <a href="/A215113/b215113.txt">Table of n, a(n) for n = 1..5000</a>

MATHEMATICA

nn = 2000; ps = Prime[Range[PrimePi[Sqrt[nn]]]]; t = Flatten[Table[ ps[[i]]^2 + ps[[j]]^2, {i, Length[ps]}, {j, i, Length[ps]}]]; t =

Select[t, # <= nn &]; PrimeNu[Sort[Transpose[Select[Tally[t], #[[2]] == 1 &]][[1]]]] (* G. C. Greubel, May 16 2017 *)

STATUS

approved

editing

#11 by Bruno Berselli at Mon Feb 08 10:47:11 EST 2016

STATUS

proposed

approved

#10 by Michel Marcus at Mon Feb 08 10:40:34 EST 2016

STATUS

editing

proposed

#9 by Michel Marcus at Mon Feb 08 10:40:29 EST 2016

FORMULA

a(n) = A001221(A214723(n)). - Michel Marcus, Feb 08 2016

CROSSREFS

Cf. A001221, A214723.

STATUS

approved

editing

#8 by N. J. A. Sloane at Fri Aug 03 14:35:55 EDT 2012

STATUS

proposed

approved

#7 by Vladimir Shevelev at Fri Aug 03 13:29:17 EDT 2012

STATUS

editing

proposed

#6 by Vladimir Shevelev at Fri Aug 03 13:29:08 EDT 2012

NAME

a(n) is the number of different prime divisors of A214723(n).

STATUS

approved

editing

#5 by N. J. A. Sloane at Fri Aug 03 13:28:05 EDT 2012

STATUS

editing

approved