A115210 a(0)=0. a(n) = number of earlier terms of the sequence which when added to n produce a composite number.

0, 0, 0, 0, 4, 1, 5, 2, 7, 7, 7, 6, 7, 7, 13, 13, 8, 11, 13, 14, 19, 19, 14, 15, 13, 23, 23, 23, 20, 21, 16, 25, 28, 27, 21, 32, 24, 29, 30, 31, 24, 32, 34, 33, 38, 37, 29, 35, 34, 43, 41, 43, 38, 43, 35, 47, 46, 49, 44, 44, 35, 54, 52, 52, 49, 52, 42, 55, 56, 55, 56, 57, 54, 59

Offset

0,5

Links

G. C. Greubel, Table of n, a(n) for n = 0..10000

Example

Adding 6 to the first 6 terms (terms 0 through 5) of the sequence gives [6,6,6,6,10,7]. Of these terms, five are composite, so a(6) = 5.

Mathematica

a = {0, 0, 0, 0}; For[n = 4, n < 10001, n++, in = 0; For[j = 1, j < Length[a] + 1, j++, If[! PrimeQ[n + a[[j]]], in++]]; AppendTo[a, in]];
a (* G. C. Greubel, Feb 05 2016 *)

Prog

(PARI) seq=vector(200); print1(0, ", "); for(j=1, 190, count=0; for(k=0, j-1, if(isprime(j+seq[k+1])==0 && (j+seq[k+1])>1, count=count+1; )); seq[j+1]=count; print1(seq[j+1], ", ")) \\ Matthew Conroy, Feb 07 2006

Crossrefs

Cf. A115207, A115208, A115209.

Sequence in context: A168230 A080414 A067061 * A199150 A329215 A214892

Adjacent sequences: A115207 A115208 A115209 * A115211 A115212 A115213

Keyword

nonn

Author

Leroy Quet, Jan 16 2006

Extensions

More terms from Matthew Conroy, Feb 07 2006

Status

approved