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A115707 Pentagonal numbers (A000326) whose digit reversal is a prime. 1


%S 5,35,70,92,145,376,1520,1820,3577,3725,7526,9322,9560,10045,10292,

%T 13490,14065,16801,17767,18760,32782,34126,34580,36895,38320,38801,

%U 39772,73151,74482,76501,78547,91390,93625,94376,98176,100492,101270

%N Pentagonal numbers (A000326) whose digit reversal is a prime.

%e 145 is the 10th pentagonal number and 541 is prime.

%t Select[Table[n (3n-1)/2,{n,400}],PrimeQ[FromDigits[Reverse[ IntegerDigits[ #]]]]&] (* _Harvey P. Dale_, Feb 23 2011 *)

%Y Cf. A000326, A115706.

%K nonn,base

%O 1,1

%A _Giovanni Resta_, Jan 31 2006

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Last modified December 3 15:34 EST 2021. Contains 349463 sequences. (Running on oeis4.)