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A176256 Numbers of the form 4k+1 with least prime divisor of the form 4m-1. 7
9, 21, 33, 45, 49, 57, 69, 77, 81, 93, 105, 117, 121, 129, 133, 141, 153, 161, 165, 177, 189, 201, 209, 213, 217, 225, 237, 249, 253, 261, 273, 285, 297, 301, 309, 321, 329, 333, 341, 345, 357, 361, 369, 381, 393, 405, 413, 417, 429, 437, 441, 453, 465, 469 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

By definition, all terms are composite numbers.

Cannot be the Hypotenuse of a primitive Pythagorean triangle. - Robert G. Wilson v, Mar 16 2014

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

MATHEMATICA

fQ[n_] := Mod[ n, 4] == 1 && Mod[ FactorInteger[n][[1, 1]], 4] == 3; Select[Range@470, fQ] (* Robert G. Wilson v, Apr 08 2014 *)

PROG

(PARI) isok(n) = ((n % 4) == 1) && (f = factor(n)) && ((f[1, 1] % 4) == 3); \\ Michel Marcus, Mar 16 2014

CROSSREFS

Cf. A176255, A002148, A002145, A016813, A004767.

Complement of A020882 in 1 == Mod 4.

Sequence in context: A133929 A325573 A086470 * A017629 A216240 A176258

Adjacent sequences:  A176253 A176254 A176255 * A176257 A176258 A176259

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Apr 13 2010

EXTENSIONS

More terms from Michel Marcus, Mar 16 2014

STATUS

approved

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Last modified June 1 07:40 EDT 2020. Contains 334759 sequences. (Running on oeis4.)