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Search: id:A017197
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| 3, 12, 21, 30, 39, 48, 57, 66, 75, 84, 93, 102, 111, 120, 129, 138, 147, 156, 165, 174, 183, 192, 201, 210, 219, 228, 237, 246, 255, 264, 273, 282, 291, 300, 309, 318, 327, 336, 345, 354, 363, 372, 381, 390, 399, 408, 417, 426, 435, 444, 453, 462, 471, 480
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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Numbers whose digital root is 3. - Cino Hilliard (hillcino368(AT)hotmail.com), Dec 26 2006
General form: (q*n+1)*q q=2=A016825, q=3=A017197, q=4=A119413, ... [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Feb 16 2009]
For all n, a(n) is not a^2+b^2. [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 27 2009]
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LINKS
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Tanya Khovanova, Recursive Sequences
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FORMULA
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a(n) = 9 + a(n-1). a(n) = 3*A016777(n). a(n) = A092292(n) + A092293(n) + A092296(n). Sum_{n>=0} (-1)^n / a(n) = (Pi / sqrt(3) + ln(2))/ 9. G.f. : 3*(1+2*x) / (1-x)^2. - DELEHAM Philippe (kolotoko(AT)wanadoo.fr), Mar 10 2004
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MATHEMATICA
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q=3; lst={}; Do[AppendTo[lst, (q*n+1)*q], {n, 0, 5!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Feb 16 2009]
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PROGRAM
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(PARI) threesome(n) = { local(x, ln, j, f); for(x=1, n, f=0; ln=length(Str(x)); if(droot(x)==3, print1(x", ")); ) } droot(n) = \ the digital root of a number. { local(x); x= n%9; if(x>0, return(x), return(9)) } - Cino Hilliard (hillcino368(AT)hotmail.com), Dec 26 2006
(Other) sage: [i+3 for i in range(480) if gcd(i, 9) == 9] # [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), May 20 2009]
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CROSSREFS
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Cf. A092292 A092293 A092296.
Sequence in context: A074276 A055041 A061819 this_sequence A051369 A069538 A052217
Adjacent sequences: A017194 A017195 A017196 this_sequence A017198 A017199 A017200
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms from Cino Hilliard (hillcino368(AT)hotmail.com), Dec 26 2006
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