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 A181558 Index of first occurrence of 2n in A031883, or 0 if 2n never occurs in A031883 = first differences of lucky numbers A000959. 0
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS 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: A131441 A035142 A064701 * A218883 A202963 A130315 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

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