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 A005098 Numbers n such that 4n + 1 is prime. 35
 1, 3, 4, 7, 9, 10, 13, 15, 18, 22, 24, 25, 27, 28, 34, 37, 39, 43, 45, 48, 49, 57, 58, 60, 64, 67, 69, 70, 73, 78, 79, 84, 87, 88, 93, 97, 99, 100, 102, 105, 108, 112, 114, 115, 127, 130, 135, 139, 142, 144, 148, 150, 153, 154, 160, 163, 165, 168, 169, 175, 177, 183 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Sum of i-th and j-th triangular numbers, where i=A096029(n), j=A096030(n); i.e., a(n) = A000217(A096029(n)) + A000217(A096030(n)). - Lekraj Beedassy, Jun 16 2004 For every n in the sequence, there is exactly 1 square number that can be subtracted to leave a pronic (A002378). E.g., 27 - 25 = 2, 99 - 9 = 90. - Jon Perry, Nov 06 2010 See A208295 for details concerning the preceding Jon Perry comment. - Wolfdieter Lang, Mar 29 2012 Solutions of the equation (4*n+1)' = 1, where n' is the arithmetic derivative of n. - Paolo P. Lava, Jan 03 2013 a(k) appears in the o.g.f. for floor(A002144(k)*n^2/4), n >= 0, for k >= 1:  x*(a(k)*(1 + x^2) + b(k)*x)/((1 - x)^3*(1 + x)), together with b(k) = (A002144(k) + 1)/2 = A119681(k). - Wolfdieter Lang, Aug 07 2013 LINKS T. D. Noe and Zak Seidov, Table of n, a(n) for n = 1..10000 (First 1000 terms from T. D. Noe). Eric Weisstein's World of Mathematics, Wilson's Theorem FORMULA a(n) = (A002144(n)-1)/4. MAPLE a := []; for n from 1 to 500 do if isprime(4*n+1) then a := [op(a), n]; fi; od: A005098 := n->a[n]; MATHEMATICA Select[Range, PrimeQ[4# + 1] &] (* Harvey P. Dale, Apr 20 2011 *) PROG (MAGMA) [n: n in [0..10000] | IsPrime(4*n+1)] // Vincenzo Librandi, Nov 18 2010 (PARI) is(n)=isprime(4*n+1) \\ Charles R Greathouse IV, Nov 20 2012 (Haskell) a005098 = (`div` 4) . (subtract 1) . a002144 -- Reinhard Zumkeller, Mar 17 2013 CROSSREFS See A002144 for the actual primes. Cf. A002972, A002973, A173331, A173330, A023212. Sequence in context: A066928 A032726 A029739 * A185661 A276786 A002977 Adjacent sequences:  A005095 A005096 A005097 * A005099 A005100 A005101 KEYWORD nonn,nice,easy AUTHOR EXTENSIONS More terms from Ray Chandler, Jun 26 2004 Edited by Charles R Greathouse IV, Mar 17 2010 STATUS approved

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Last modified December 15 00:30 EST 2019. Contains 329988 sequences. (Running on oeis4.)