A095248 a(n) = least k > 0 such that n-th partial sum is divisible by n if and only if n is not prime.

1, 2, 1, 4, 1, 3, 1, 3, 2, 2, 1, 3, 1, 3, 2, 2, 1, 3, 1, 3, 2, 2, 1, 3, 2, 2, 2, 2, 1, 3, 1, 3, 2, 2, 2, 2, 1, 3, 2, 2, 1, 3, 1, 3, 2, 2, 1, 3, 2, 2, 2, 2, 1, 3, 2, 2, 2, 2, 1, 3, 1, 3, 2, 2, 2, 2, 1, 3, 2, 2, 1, 3, 1, 3, 2, 2, 2, 2, 1, 3, 2, 2, 1, 3, 2, 2, 2, 2, 1, 3, 2, 2, 2, 2, 2, 2, 1, 3, 2, 2, 1, 3, 1, 3, 2

Offset

1,2

Links

Antti Karttunen, Table of n, a(n) for n = 1..10000

Example

n = 1 is not prime, k = 1 results in first partial sum 1 divisible by 1 as required, so a(1) = 1.
n = 2 is prime, k = 1 results in second partial sum 2 divisible by 2 and is excluded, but k = 2 results in second partial sum 3 not divisible by 2 as required, so a(2) = 2.

Prog

(PARI) {m=105; s=0; for(n=1, m, k=1; if(isprime(n), while((s+k)%n==0, k++), while((s+k)%n>0, k++)); print1(k, ", "); s=s+k)}

Crossrefs

Sequence in context: A124331 A242885 A181157 * A122458 A329644 A256578

Adjacent sequences: A095245 A095246 A095247 * A095249 A095250 A095251

Keyword

nonn

Author

Amarnath Murthy, Jun 17 2004

Extensions

Edited and extended by Klaus Brockhaus, Jun 19 2004

Status

approved