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A131229
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Numbers congruent to {1,7} mod 10.
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3
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1, 7, 11, 17, 21, 27, 31, 37, 41, 47, 51, 57, 61, 67, 71, 77, 81, 87, 91, 97, 101, 107, 111, 117, 121, 127, 131, 137, 141, 147, 151, 157, 161, 167, 171, 177, 181, 187, 191, 197, 201, 207, 211, 217, 221, 227, 231, 237, 241, 247, 251, 257, 261, 267, 271, 277, 281
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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FORMULA
| Row sums of triangle A131228.
a(n)=-3+Sum_{k=0..n}{5-(-1)^k} - Paolo P. Lava (paoloplava(AT)gmail.com), Nov 05 2007
a(n) = a(n-2)+10 = 5*n+((-1)^n-7)/2. O.g.f.: x*(1+6*x+3*x^2)/((-1+x)^2*(1+x)) . - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 17 2008
a(n)=10*n-a(n-1)-12 (with a(1)=1) [From Vincenzo Librandi, Nov 23 2010]
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EXAMPLE
| 11 = a(3) = 1 mod 10.
11 = a(3) = row 4 sums, triangle A131228: (1 + 3 + 7).
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CROSSREFS
| Cf. A128174, A051340, A131228.
Sequence in context: A078497 A155048 A063639 * A092737 A072669 A108101
Adjacent sequences: A131226 A131227 A131228 * A131230 A131231 A131232
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KEYWORD
| nonn
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AUTHOR
| Gary W. Adamson (qntmpkt(AT)yahoo.com), Jun 20 2007
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EXTENSIONS
| More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 17 2008
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