The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A275156 The 108 numbers n such that n(n+1) is 17-smooth. 1
 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 20, 21, 24, 25, 26, 27, 32, 33, 34, 35, 39, 44, 48, 49, 50, 51, 54, 55, 63, 64, 65, 77, 80, 84, 90, 98, 99, 104, 119, 120, 125, 135, 143, 153, 168, 169, 175, 195, 220, 224, 242, 255, 272, 288, 324, 350, 351, 363, 374, 384, 440, 441, 539, 560, 594, 624, 675, 714, 728, 832, 935, 1000, 1088, 1155, 1224, 1274, 1700, 1715, 2057, 2079, 2400, 2430, 2499, 2600, 3024, 4095, 4224, 4374, 4913, 5831, 6655, 9800, 10647, 12375, 14399, 28560, 31212, 37179, 123200, 194480, 336140 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS This is the 7th row of the table A138180. REFERENCES See A002071. LINKS Table of n, a(n) for n=1..108. MATHEMATICA pMax = 17; smoothMax = 10^12; smoothNumbers[p_?PrimeQ, max_] := Module[{a, aa, k, pp, iter}, k = PrimePi[p]; aa = Array[a, k]; pp = Prime[Range[k]]; iter = Table[{a[j], 0, PowerExpand@Log[pp[[j]], max/Times @@ (Take[pp, j - 1]^Take[aa, j - 1])]}, {j, 1, k}]; Table[Times @@ (pp^aa), Sequence @@ iter // Evaluate] // Flatten // Sort]; Select[(Sqrt[1 + 4*smoothNumbers[pMax, smoothMax]] - 1)/2, IntegerQ] PROG (PARI) is(n)=my(t=510510); n*=n+1; while((t=gcd(n, t))>1, n/=t); n==1 \\ Charles R Greathouse IV, Nov 13 2016 CROSSREFS Cf. A002071, A145604, A138180, A145605, A002072, A085152, A085153, A252493, A252492. Sequence in context: A291149 A363748 A322463 * A188459 A146295 A123719 Adjacent sequences: A275153 A275154 A275155 * A275157 A275158 A275159 KEYWORD nonn,fini,full AUTHOR Jean-François Alcover, Nov 13 2016 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 2 19:53 EDT 2024. Contains 374875 sequences. (Running on oeis4.)