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Search: id:A125227
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| 1, 3, 7, 9, 21, 27, 49, 57, 63, 81, 147, 171, 189, 219, 243, 301, 343, 399, 441, 513, 567, 657, 729, 889, 903, 1029, 1083, 1197, 1323, 1533, 1539, 1701, 1971, 2107, 2187, 2359, 2401, 2667, 2709, 2793, 3087, 3249, 3591, 3969, 4161, 4401, 4599, 4617, 5103, 5913
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OFFSET
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3,2
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COMMENT
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A014141(n) are the numbers n such that n divides s(n), where s(1)=1, s(k)=2*s(k-1)+k. A014741(n) is divisible by 6 for n>2.
All powers of 3 are terms. All powers of 7 are terms. The prime divisors of terms of this sequence (for n up to 10^6) in order of their first appearance are {3,7,19,73,43,127,337,163,379,571,5419,487,2593,439,1459,431,883}. The sequence is multiplicative in the sense that if two numbers k and m are terms, then k*m is too.
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EXAMPLE
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A014141(n) begins {1, 2, 6, 18, 42, 54, 126, 162, 294, 342, 378, 486, ...}.
Thus a(3) = A014141(3)/6 = 6/6 = 1, a(4) = A014141(4)/6 = 18/6 = 3.
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MATHEMATICA
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Select[Range[3, 1000000], PowerMod[2, #+1, # ]==2&]/6
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CROSSREFS
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Cf. A014741, A000295, A086787.
Sequence in context: A056652 A014959 A057233 this_sequence A057286 A056745 A057263
Adjacent sequences: A125224 A125225 A125226 this_sequence A125228 A125229 A125230
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KEYWORD
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nonn
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AUTHOR
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Alexander Adamchuk (alex(AT)kolmogorov.com), Jan 15 2007
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