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A051697
Closest prime to n (break ties by taking the smaller prime).
24
2, 2, 2, 3, 3, 5, 5, 7, 7, 7, 11, 11, 11, 13, 13, 13, 17, 17, 17, 19, 19, 19, 23, 23, 23, 23, 23, 29, 29, 29, 29, 31, 31, 31, 31, 37, 37, 37, 37, 37, 41, 41, 41, 43, 43, 43, 47, 47, 47, 47, 47, 53, 53, 53, 53, 53, 53, 59, 59, 59, 59, 61, 61, 61, 61, 67, 67, 67, 67, 67, 71, 71
OFFSET
0,1
Eric Weisstein's World of Mathematics, Nearest Prime
EXAMPLE
Closest primes to 0,1,2,3,4 are 2,2,2,3,3.
MATHEMATICA
a[n_] := (np = NextPrime[n]; pp = Prime[PrimePi[np] - 1]; Which[np > 2n-pp, pp, np < 2n-pp, np, True, pp]); a[0] = a[1] = 2; Table[a[n], {n, 0, 71}] (* Jean-François Alcover, Jul 28 2011 *)
PROG
(PARI) a(n)=if(n<3, return(2)); my(p=precprime(n), q=nextprime(n)); if(q-n<n-p, q, p) \\ Charles R Greathouse IV, Apr 28 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
More terms from James A. Sellers
STATUS
approved

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Last modified September 20 10:13 EDT 2024. Contains 376068 sequences. (Running on oeis4.)