A335774 Numbers k such that in prime factorization of k the second smallest factor is 7.

14, 21, 28, 35, 56, 63, 98, 112, 147, 154, 175, 182, 189, 196, 224, 231, 238, 245, 266, 273, 308, 322, 357, 364, 385, 392, 399, 406, 434, 441, 448, 455, 476, 483, 518, 532, 567, 574, 595, 602, 609, 616, 644, 651, 658, 665, 686, 693, 728, 742, 777, 784, 805, 812, 819, 826, 854, 861

Offset: 1

Author

Zak Seidov, Jun 22 2020

Keywords

• nonn

Comments

Trivially, all terms are multiples of 7. Also terms are divisible by 2 or 3 or 5, and by any number of primes > 7.

Examples

			14 = 2*7, 28 = 2*2*7, 35 = 5*7, 56 = 2^3*7, 63 = 3*3*7, 147 = 3*7*7, 154 = 2*7*11.
		

Links

• Ray Chandler, Table of n, a(n) for n = 1..1000
• Index entries for linear recurrences with constant coefficients, signature (1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1).

Crossrefs

Cf. A008589 (multiples of 7).

Subsequence of A080671.

Programs

Mathematica

Select[Range[14, 1000], 1 < Length[fi = FactorInteger[#]] && 7 == fi[[2, 1]] &]