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%I #38 Sep 08 2022 08:45:12
%S 11,31,61,101,151,211,281,661,911,1051,1201,1361,1531,1901,2311,2531,
%T 3001,3251,3511,4651,5281,6301,6661,7411,9461,9901,12251,13781,14851,
%U 15401,18301,18911,19531,20161,22111,24151,24851,25561,27011,27751
%N Primes of the form 5k^2 + 5k + 1.
%C Or, primes obtained as a concatenation of a triangular number and 1.
%C Centered decagonal primes. - _Paul Muljadi_, Oct 04 2005
%H Vincenzo Librandi, <a href="/A090562/b090562.txt">Table of n, a(n) for n = 1..5000</a>
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Centered_decagonal_number">Centered decagonal number.</a>
%t Select[5(#^2 - #) + 1 & /@ Range[75], PrimeQ[ # ] &] (* _Robert G. Wilson v_, Oct 10 2005 *)
%o (Magma) [a: n in [0..100] | IsPrime(a) where a is 5*n^2 + 5*n + 1]; // _Vincenzo Librandi_, Dec 13 2011
%Y Cf. A090563, A062786.
%K easy,nonn
%O 1,1
%A _Amarnath Murthy_, Dec 11 2003
%E Edited and extended by _Robert G. Wilson v_, Oct 10 2005
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