A096879 a(1) = 1; for n > 1: a(n) = least multiple m of n such that m is coprime to n+1 and the absolute difference of a(n) and a(n-1) is a prime distinct from all earlier such differences of consecutive terms.

1, 4, 9, 16, 5, 18, 35, 16, 63, 10, 77, 36, 13, 56, 135, 32, 289, 18, 209, 100, 63, 176, 115, 144, 175, 26, 405, 56, 319, 90, 31, 128, 495, 34, 245, 72, 481, 38, 351, 40, 779, 126, 43, 704, 45, 184, 47, 240, 637, 50, 357, 520, 53, 486, 55, 392, 285, 58, 767, 120, 793, 992

Offset

1,2

Comments

Suggested by A096134.

Primes arising as absolute first differences are given in A096880.

Links

Table of n, a(n) for n=1..62.

Example

a(8) has to be a multiple of 8; 16 is the smallest one that satisfies all conditions: 16 is coprime to 9, abs(a(7) - 16) = 19 is prime and distinct from all earlier absolute differences 3, 5, 7, 11, 13, 17. Hence a(8) = 16.

Prog

(PARI) {print1(a=1, ", "); v=Set([]); for(n=2, 62, k=1; b=1; while(b, m=k*n; p=abs(m-a); if(gcd(m, n+1)==1&&isprime(p)&&setsearch(v, p)==0, v=setunion(v, Set(p)); print1(m, ", "); a=m; b=0, k++)))}

Crossrefs

Cf. A096134, A096880.

Sequence in context: A070643 A070442 A086957 * A070441 A070440 A368103

Adjacent sequences: A096876 A096877 A096878 * A096880 A096881 A096882

Keyword

nonn

Author

Klaus Brockhaus, Jul 14 2004

Status

approved