A074038 If n is the k-th single (i.e., non-twin) prime then a(n) = k, otherwise a(n) = 0.

0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 8, 0, 0, 0, 0, 0, 9, 0, 0, 0, 0, 0, 0, 0, 10, 0, 0

Offset

1,23

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Formula

A007510(a(n)) = n.

Mathematica

upto = 100;
A074038list[upto_] := Module[{k = 0, v = Table[0, {upto}], n},
    For[n = 1, n <= upto, n++, If[PrimeQ[n] && (2 == n ||
    ((!PrimeQ[n-2]) && (!PrimeQ[n+2]))), k++; v[[n]] = k,
    v[[n]] = 0]]; v];
v074038 = A074038list[upto];
a[n_] := v074038[[n]];
Table[a[n], {n, 1, upto}] (* Jean-François Alcover, Dec 03 2021, after PARI code *)

Prog

(PARI)
up_to = 65537;
A074038list(up_to) = { my(k=0, v=vector(up_to)); for(n=1, up_to, if(isprime(n)&&(2==n||((!isprime(n-2))&&(!isprime(n+2)))), k++; v[n]=k, v[n] = 0)); (v); };
v074038 = A074038list(up_to);
A074038(n) = v074038[n];

Crossrefs

Cf. A007510, A049084, A074039.

Sequence in context: A379505 A379504 A083928 * A204843 A204853 A303709

Adjacent sequences: A074035 A074036 A074037 * A074039 A074040 A074041

Keyword

nonn

Author

Reinhard Zumkeller, Aug 13 2002

Status

approved