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 A248877 a(1) = 23, a(2) = 71, a(n) = 3*a(n-1) - 2*a(n-2) for n>2. 1
 23, 71, 167, 359, 743, 1511, 3047, 6119, 12263, 24551, 49127, 98279, 196583, 393191, 786407, 1572839, 3145703, 6291431, 12582887, 25165799, 50331623, 100663271, 201326567, 402653159, 805306343, 1610612711, 3221225447, 6442450919, 12884901863, 25769803751 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The first 6 terms are prime, so are the 9th, 10th, 13th, 14th, 15th, 18th, 20th, and 26th. Any term of the form a(7+n*10) appears to be divisible by 11. Any term of the form a(11+n*12) appears to be divisible by 13. Any term of the form a(1+n*22) appears to be divisible by 23. Any term that is not prime appears to have its factors recurring periodically in the sequence as factors of higher terms. LINKS Colin Barker, Table of n, a(n) for n = 1..1000 Index entries for linear recurrences with constant coefficients, signature (3,-2). FORMULA a(n) = 3*2^(n+3)-25 = A007283(n+3)-25. a(n+1) = a(n)+3*2^(n+3) with a(1) = 23. a(n) = 3*a(n-1)-2*a(n-2). - Colin Barker, Mar 05 2015 G.f.: x*(2*x+23) / ((x-1)*(2*x-1)). - Colin Barker, Mar 05 2015 MATHEMATICA Table[3*2^(n + 3) - 25, {n, 1, k}] PROG (PARI) Vec(x*(2*x+23)/((x-1)*(2*x-1)) + O(x^100)) \\ Colin Barker, Mar 05 2015 (MAGMA) [3*2^(n + 3) - 25: n in [1..30]]; // Vincenzo Librandi, Mar 08 2015 CROSSREFS Sequence in context: A154619 A142405 A139962 * A321356 A139878 A035072 Adjacent sequences:  A248874 A248875 A248876 * A248878 A248879 A248880 KEYWORD nonn,easy AUTHOR Zeid Ghalyoun, Mar 05 2015 STATUS approved

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Last modified January 26 14:08 EST 2020. Contains 331280 sequences. (Running on oeis4.)