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

Author

Vladimir Joseph Stephan Orlovsky, Apr 16 2011

Keywords

• nonn

Examples

			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).
		

Crossrefs

Cf. A002808, A161945.

Programs

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]

Extensions

Name clarified by Tanya Khovanova, Jun 23 2021