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A090562 Primes of the form 5k^2 + 5k + 1 13
11, 31, 61, 101, 151, 211, 281, 661, 911, 1051, 1201, 1361, 1531, 1901, 2311, 2531, 3001, 3251, 3511, 4651, 5281, 6301, 6661, 7411, 9461, 9901, 12251, 13781, 14851, 15401, 18301, 18911, 19531, 20161, 22111, 24151, 24851, 25561, 27011, 27751 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Or, primes obtained as a concatenation of a triangular number and 1.

Centered decagonal primes. - Paul Muljadi, Oct 04 2005

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..5000

Wikipedia, Centered decagonal number.

MATHEMATICA

Select[5(#^2 - #) + 1 & /@ Range[75], PrimeQ[ # ] &] (* Robert G. Wilson v *)

PROG

(MAGMA) [a: n in [0..100] | IsPrime(a) where a is 5*n^2 + 5*n + 1]; // Vincenzo Librandi, Dec 13 2011

CROSSREFS

Cf. A090563.

Sequence in context: A202007 A125239 A062786 * A174244 A136061 A090233

Adjacent sequences:  A090559 A090560 A090561 * A090563 A090564 A090565

KEYWORD

easy,nonn

AUTHOR

Amarnath Murthy, Dec 11 2003

EXTENSIONS

Edited and extended by Robert G. Wilson v, Oct 10 2005

STATUS

approved

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Last modified December 2 17:19 EST 2016. Contains 278681 sequences.