A115207 - OEIS

A115207

a(1)=1. a(n) = number of earlier terms of the sequence which when added to n produce a composite number.

1, 0, 1, 1, 3, 2, 5, 5, 7, 4, 8, 5, 10, 9, 11, 10, 14, 10, 13, 16, 14, 16, 18, 18, 19, 20, 16, 20, 21, 23, 23, 25, 23, 27, 30, 23, 27, 27, 31, 27, 33, 31, 31, 33, 37, 31, 41, 31, 41, 39, 40, 34, 43, 45, 47, 36, 45, 40, 50, 43, 51, 44, 47, 50, 56, 41, 56, 53, 55, 47, 61, 55, 60, 57

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,5

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..10000

EXAMPLE

Adding 7 to the first 6 terms of the sequence gives [8,7,8,8,10,9]. Of these terms, five are composite, so a(7) = 5.

MATHEMATICA

a = {1, 0}; For[n = 3, 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); seq[1]=1; print1(1, ", "); for(j=1, 190, count=0; for(k=1, j, if(isprime(j+1+seq[k])==0 && (j+1+seq[k])>1, count=count+1; )); seq[j+1]=count; print1(seq[j+1], ", ")) \\ Matthew Conroy, Feb 09 2006

CROSSREFS

Cf. A115208, A115209, A115210.

Sequence in context: A196438 A019828 A289627 * A093048 A141732 A325695

Adjacent sequences: A115204 A115205 A115206 * A115208 A115209 A115210

KEYWORD

nonn

AUTHOR

Leroy Quet, Jan 16 2006

EXTENSIONS

More terms from Matthew Conroy, Feb 09 2006

STATUS

approved