A181558 Index of first occurrence of 2n in A031883, or 0 if 2n never occurs in A031883 = first differences of lucky numbers A000959.

1, 2, 6, 20, 31, 14, 126, 85, 36, 145, 140, 122, 376, 231, 162, 483, 692, 600, 993, 1188, 1106, 2440, 1080, 2814, 2586, 450, 2696, 3473, 4254, 4857, 5918, 2364, 4760, 4818, 21192, 13116, 19284, 14855, 12158, 31032, 18174, 15068, 35700, 56846, 27367, 33716, 13736, 16746, 103292, 8541

Offset

1,2

Links

Table of n, a(n) for n=1..50.

Formula

a(n) = min { k | A031883(k)=2n } = min { k | A000959(k+1)=A000959(k)+2n }.

Example

a(1)=1 is the least index i such that A000959(i)+2*1 = A000959(i+1), since A000959(1) = 1 and A000959(2) = 3.
a(2)=2 is the least index i such that A000959(i)+2*2 = A000959(i+1), since A000959(2) = 3 and A000959(3) = 7.
a(3)=6 is the least index i such that A000959(i)+2*3 = A000959(i+1); indeed A000959(7) - A000959(6) = 21 - 15 is the earliest gap of 6 in A000959.

Prog

(PARI) a(n) = for( i=1, 1e9, A031883[i]==2*n & return(i)) /* will issue an error if 2n is not found in A031883 */

Crossrefs

Cf. A038664 (analog for primes).

Sequence in context: A035142 A064701 A368249 * A218883 A353699 A202963

Adjacent sequences: A181555 A181556 A181557 * A181559 A181560 A181561

Keyword

nonn

Author

M. F. Hasler, Oct 31 2010

Extensions

a(20)-a(50) from Nathaniel Johnston, Nov 15 2010

Status

approved