A087566 - OEIS

A087566

a(n) = index of the first occurrence of n in A087565, or 0 if n is not a term of A087565.

1, 3, 9, 0, 7, 26, 32, 35, 29, 11, 109, 31, 95, 43, 394, 67, 127, 23, 55, 224, 107, 265, 237, 92, 158, 386, 233, 989, 401, 1229, 714, 197, 380, 384, 541, 142, 179, 376, 908, 149, 723, 963, 169, 2187, 909, 919, 519, 360, 674, 1376, 636, 643, 2468, 1284, 504, 781

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OFFSET

0,2

COMMENTS

Smallest k such that n is the smallest number for which k*(k+1)*(k+2)...(k+n) + 1 is prime.

a(3) = 0 since 3 is not a term of A087565 because k*(k+1)*(k+2)*(k+3) + 1 is a square for every k.

LINKS

Table of n, a(n) for n=0..55.

EXAMPLE

a(1) = 3 since 1+1 is prime, 2+1 is prime, 3+1 is composite, 3*(3+1)+1 = 13 is prime.

PROG

(PARI) {p=55; a=2500; v=vector(p+1); for(n=1, a, k=0; m=n; while(!isprime(m+1, 1)&& k<=p+1, k++; m=m*(n+k)); if(k<=p, if(v[k+1]<1, v[k+1]=n))); for(j=1, p+1, print1(v[j], ", "))}

CROSSREFS

Cf. A087564, A087565.

Sequence in context: A019832 A244337 A338033 * A011337 A195456 A021723

Adjacent sequences: A087563 A087564 A087565 * A087567 A087568 A087569

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Sep 15 2003

EXTENSIONS

Edited and extended by Klaus Brockhaus, Sep 20 2003

STATUS

approved