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 A001751 Primes together with primes multiplied by 2. 18
 2, 3, 4, 5, 6, 7, 10, 11, 13, 14, 17, 19, 22, 23, 26, 29, 31, 34, 37, 38, 41, 43, 46, 47, 53, 58, 59, 61, 62, 67, 71, 73, 74, 79, 82, 83, 86, 89, 94, 97, 101, 103, 106, 107, 109, 113, 118, 122, 127, 131, 134, 137, 139, 142, 146, 149, 151, 157, 158, 163, 166 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For n > 1, a(n) is position of primes in A026741. For n > 1, a(n) is the position of the ones in A046079. - Ant King, Jan 29 2011 A251561(a(n)) != a(n). - Reinhard Zumkeller, Dec 27 2014 Number of terms <= n is pi(n) + pi(n/2). - Robert G. Wilson v, Aug 04 2017 Number of terms <=10^k: 7, 40, 263, 1898, 14725, 120036, 1013092, 8762589, 77203401, 690006734, 6237709391, 56916048160, 523357198488, 4843865515369, ..., . - Robert G. Wilson v, Aug 04 2017 LINKS T. D. Noe, Table of n, a(n) for n = 1..10000 MATHEMATICA Select[Range[163], Or[PrimeQ[#], PrimeQ[1/2 #]] &] (* Ant King, Jan 29 2011 *) upto=200; With[{pr=Prime[Range[PrimePi[upto]]]}, Select[Sort[Join[pr, 2pr]], # <= upto&]] (* Harvey P. Dale, Sep 23 2014 *) PROG (Haskell) a001751 n = a001751_list !! (n-1) a001751_list = 2 : filter (\n -> (a010051 \$ div n \$ gcd 2 n) == 1) [1..] -- Reinhard Zumkeller, Jun 20 2011 (corrected, improved), Dec 17 2010 (PARI) isA001751(n)=isprime(n/gcd(n, 2)) || n==2 (PARI) list(lim)=vecsort(concat(primes(primepi(lim)), 2* primes(primepi(lim\2)))) \\ Charles R Greathouse IV, Oct 31 2012 CROSSREFS Union of A001747 and A000040. Subsequence of A039698 and of A033948. Cf. A026741, A046079, A178156, A251561. Sequence in context: A205666 A245809 A064295 * A191927 A116000 A251595 Adjacent sequences: A001748 A001749 A001750 * A001752 A001753 A001754 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified March 27 11:48 EDT 2023. Contains 361570 sequences. (Running on oeis4.)