A298861 -id:A298861 - cp's OEIS frontend

A298862 Rank of n-th twice-prime when all the primes and twice-primes are jointly ranked.

3, 5, 7, 10, 13, 15, 18, 20, 23, 26, 29, 33, 35, 37, 39, 43, 47, 48, 51, 54, 55, 59, 61, 64, 69, 72, 73, 75, 76, 78, 85, 87, 91, 93, 97, 98, 102, 104, 106, 108, 112, 114, 118, 120, 122, 124, 129, 134, 136, 138, 141, 143, 145, 149, 152, 155, 156, 158, 160

Offset: 1

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Clark Kimberling, Feb 13 2018

nonn
easy

			A001751 = ordered sequence of primes and twice-primes:  2,3,4,5,6,7,10,... in which twice-primes occupy ranks 3,5,7,...

Clark Kimberling, Table of n, a(n) for n = 1..1000

Cf. A000040, A001751, A298861 (complement).

z = 1000; u = Prime[Range[z]]; w = Take[Union[u, 2 u], z];
p[n_] := If[MemberQ[u, w[[n]]], 0, 1];
Take[w, z];  (* A001751 *)
t = Table[p[n], {n, 1, z}];
Flatten[Position[t, 0]];  (* A298861 *)
Flatten[Position[t, 1]];  (* A298862 *)

cp's OEIS Frontend

A298862 Rank of n-th twice-prime when all the primes and twice-primes are jointly ranked.

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