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A228184 Numbers k such that k^2 + k + 41 is semiprime. 3
40, 41, 44, 49, 56, 65, 76, 81, 82, 84, 87, 89, 91, 96, 102, 104, 109, 117, 121, 122, 123, 126, 127, 130, 136, 138, 140, 143, 147, 155, 159, 161, 162, 163, 164, 170, 172, 173, 178, 184, 185, 186, 187, 190, 201, 204, 205, 207, 208, 209, 213, 215, 216, 217, 218 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Subsequence of A007634. Numbers in A007634 but not in here are 420, 431, 491, 492, 514, 533, 573, etc. (A097822). - R. J. Mathar, Aug 17 2013

LINKS

Shyam Sunder Gupta, Table of n, a(n) for n = 1..4760

EXAMPLE

a(3) = 44 is in the sequence because 44^2 + 44 + 41 = 43*47 is semiprime.

MATHEMATICA

a = {}; Do[

If[PrimeOmega[x^2 + x + 41] == 2, AppendTo[a, x]], {x, 1, 500}]; a

CROSSREFS

Cf. A002837, A001358, A007634.

Sequence in context: A165861 A082763 A007634 * A128843 A214563 A111167

Adjacent sequences:  A228181 A228182 A228183 * A228185 A228186 A228187

KEYWORD

nonn,less

AUTHOR

Shyam Sunder Gupta, Aug 15 2013

STATUS

approved

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Last modified September 18 20:58 EDT 2021. Contains 347536 sequences. (Running on oeis4.)