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 A091308 Primes in A038395 (concatenate first n odd numbers in reverse order). 1
 31, 737169676563615957555351494745434139373533312927252321191715131197531, 12312111911711511311110910710510310199979593918987858381797775737169676563615957555351494745434139373533312927252321191715131197531 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Among the first 72 terms only three terms are prime SmBackConOdd(2), SmBackConOdd(37) and SmBackConOdd(62), found by Micha Fleuren. The next term (a(4)) has 1172 digits. - Harvey P. Dale, Jul 12 2022 a(5) = A038395(2717) has 10313 digits. - Robert Israel, Apr 14 2024 LINKS Table of n, a(n) for n=1..3. M. Fleuren, Smarandache Back Concatenated Odds. Mathematics StackExchange, Is it known whether or not OEIS sequence A091308 is finite? MAPLE x:= 1: d:= 1: count:= 0: R:= NULL: for i from 2 while count < 5 do x:= (2*i-1)*10^d + x; d:= d + ilog10(2*i-1)+1; if isprime(x) then count:= count+1; R:= R, x; fi; od: R; # Robert Israel, Apr 14 2024 MATHEMATICA Select[Table[FromDigits[Flatten[IntegerDigits/@Range[n, 1, -2]]], {n, 1, 341, 2}], PrimeQ] (* Harvey P. Dale, Jul 12 2022 *) CROSSREFS Cf. A038395. Sequence in context: A216791 A324268 A145210 * A023927 A345676 A240253 Adjacent sequences: A091305 A091306 A091307 * A091309 A091310 A091311 KEYWORD nonn,bref,base AUTHOR M. Grete (martha.grete(AT)web.de), Feb 21 2004 EXTENSIONS Definition corrected by XU Pingya, Mar 16 2017 STATUS approved

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Last modified May 17 19:49 EDT 2024. Contains 372607 sequences. (Running on oeis4.)