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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
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
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.)