A189119 Sums k of three consecutive odd numbers, all of which are composite, such that k is also the smallest in a set of three consecutive odd numbers, all of which are composite.

621, 867, 891, 897, 1023, 1239, 1413, 1587, 1881, 2091, 2115, 2145, 2169, 2403, 2451, 2505, 2601, 2769, 2871, 2889, 3003, 3129, 3171, 3231, 3237, 3243, 3399, 3417, 3423, 3435, 3441, 3471, 3477, 3501, 3807, 3813, 3933, 3993, 4029

Offset

1,1

Links

Table of n, a(n) for n=1..39.

Example

621 is a term: it is the smallest of three consecutive odd composite numbers (621 = 3^3*23, 623 = 7*89, 625 = 5^4) and is also the sum of three consecutive odd composite numbers (205 = 5*41, 207 = 3^2*23, 209 = 11*19, and 205 + 207 + 209 = 621).

Mathematica

fQ[n_]:=!PrimeQ[n]&&!PrimeQ[n+2]&&!PrimeQ[n+4];
lst1=Select[Range[3, 9000, 2], fQ];
lst2=3*Select[Range[3, 3000, 2], fQ]+6;
Intersection[lst1, lst2]

Crossrefs

Cf. A002808, A161945.

Sequence in context: A252527 A232422 A335767 * A203086 A251243 A184226

Adjacent sequences: A189116 A189117 A189118 * A189120 A189121 A189122

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Apr 16 2011

Extensions

Name clarified by Tanya Khovanova, Jun 23 2021

Status

approved