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 A258271 Decimal expansion of the sum of the reciprocal of the squares of the numbers whose digits are all even. 0
 0, 3, 6, 6, 3, 6, 0, 0, 3, 9, 7, 1, 9, 5, 2, 3, 2, 9, 5, 1, 7, 1, 8, 8, 2, 5, 0, 8, 9, 6, 7, 4, 1, 2, 4, 2, 6, 6, 2, 5, 1, 7, 3, 9, 5, 0, 3, 4, 2, 1, 1, 8, 7, 6, 0, 0, 2, 0, 0, 7, 1, 1, 3, 5, 0, 8, 5, 2, 8, 3, 3, 3, 2, 9, 3, 4, 9, 5, 1, 5, 7, 5, 8, 4, 4, 6, 5 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A rational approximation (correct up to the 9th decimal digit) is 22781/62182. Continued fraction: [0, 2, 1, 2, 1, 2, 3, 3, 1, 8, 5, 2, 1, 14,...]. LINKS EXAMPLE Decimal expansion of Sum_{k=1..oo}{1/A045926(k)^2} = 1/2^2 + 1/4^2 + 1/6^2 + 1/8^2 + 1/22^2 + 1/24^2 + 1/26^2 + ... = 0.3663600397195232951718825089674124266251739503421187600... MAPLE P:=proc(q) local a, b, k, ok, n; a:=0; for n from 2 by 2 to q do ok:=1; b:=n; for k from 1 to ilog10(n)+1 do if (b mod 10)=0 or ((b mod 10) mod 2)=1 then ok:=0; break; else b:=trunc(b/10); fi; od; if ok=1 then a:=a+(1/n)^2; fi; od; print(evalf(a, 200)); end: P(10^9); CROSSREFS Cf. A045926, A194181, A194182. Sequence in context: A323773 A309448 A016662 * A105396 A247685 A185735 Adjacent sequences:  A258268 A258269 A258270 * A258272 A258273 A258274 KEYWORD nonn,cons AUTHOR Paolo P. Lava, May 25 2015 STATUS approved

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Last modified May 20 08:58 EDT 2022. Contains 353870 sequences. (Running on oeis4.)