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A236676
The n-th term is the n-th composite if n is prime, and the n-th prime if n is not prime.
2
2, 6, 8, 7, 10, 13, 14, 19, 23, 29, 20, 37, 22, 43, 47, 53, 27, 61, 30, 71, 73, 79, 35, 89, 97, 101, 103, 107, 44, 113, 46, 131, 137, 139, 149, 151, 54, 163, 167, 173, 58, 181, 62, 193, 197, 199, 66, 223, 227, 229, 233, 239, 75, 251, 257, 263, 269, 271, 82
OFFSET
1,1
COMMENTS
See A097457 for the (maybe more natural) variant where "n-th composite"(=A002808(n)) is replaced by "n-th nonprime" (=A018252(n)).
Essentially the same as A088608. - R. J. Mathar, Feb 03 2014
LINKS
FORMULA
a(n) = A002808(n) if n is prime, a(n) = A000040(n) else.
MATHEMATICA
Module[{nn=100, prs, cmps, len}, cmps=Select[Range[nn], CompositeQ]; len= Length[ cmps]; prs=Prime[Range[len]]; Table[If[PrimeQ[n], cmps[[n]], prs[[n]]], {n, len}]] (* Harvey P. Dale, Dec 27 2022 *)
PROG
(PARI) A236676 = n->if(isprime(n), A002808(n), prime(n))
CROSSREFS
Sequence in context: A182586 A011224 A272097 * A021376 A243311 A093888
KEYWORD
nonn,changed
AUTHOR
M. F. Hasler, Jan 29 2014
STATUS
approved