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 A051697 Closest prime to n (break ties by taking the smaller prime). 22
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS 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

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Last modified October 19 14:36 EDT 2019. Contains 328222 sequences. (Running on oeis4.)