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A142347
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Nonprimes of the form (p(n)+r(n))/2, where p(n)=n-th prime and r(n)=n-th nonprime.
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0
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1, 22, 32, 42, 58, 66, 88, 99, 104, 114, 119, 144, 166, 196, 200, 214, 221, 253, 279, 287, 291, 300, 314, 326, 345, 352, 372, 400, 407, 418, 426, 442, 454, 472, 482, 502, 506, 513, 538, 556, 566, 573, 580, 590, 602, 612, 618, 625, 630, 669, 698, 708, 717, 725
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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EXAMPLE
| If n=1, then (p(1)+r(1))/2=(2+0)/2=1=a(1).
If n=10, then (p(10)+r(10))/2=(29+15)/2=22=a(2).
If n=14, then (p(14)+r(14))/2=(43+21)/2=32=a(3).
If n=17, then (p(17)+r(17))/2=(59+25)/2=42=a(4).
If n=23, then (p(23)+r(23))/2=(83+33)/2=58=a(5), etc.
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MAPLE
| Contribution from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 28 2010: (Start)
A141468 := proc(n) option remember; if n <= 2 then n-1; else for a from procname(n-1)+1 do if not isprime(a) then return a; end if; end do; end if; end proc:
for n from 1 to 300 do c := (ithprime(n)+A141468(n))/2 ; if type(c, 'integer') then if not isprime(c) then printf("%d, ", c) ; end if; end if; end do: (End)
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CROSSREFS
| Cf. A000040, A141468.
Sequence in context: A179282 A106555 A106557 * A121019 A167337 A100372
Adjacent sequences: A142344 A142345 A142346 * A142348 A142349 A142350
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KEYWORD
| nonn
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AUTHOR
| Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Sep 19 2008
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EXTENSIONS
| Corrected (119 inserted, 239 removed etc.) by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 28 2010
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