A173977 Integers k > 1 for which A020639(2*k-1) < A020639(2*k-3).

5, 8, 11, 13, 14, 17, 20, 23, 25, 26, 28, 29, 32, 35, 38, 41, 43, 44, 46, 47, 50, 53, 56, 58, 59, 62, 65, 67, 68, 71, 73, 74, 77, 80, 83, 85, 86, 88, 89, 92, 95, 98, 101, 103, 104, 107, 110, 113, 116, 118, 119, 122, 125, 127, 128, 130, 131, 133, 134, 137, 140, 143, 146, 148

Offset: 1

Author

Vladimir Shevelev, Mar 04 2010

Keywords

• nonn
• easy

Comments

Every number m == 2 (mod 3), m > 2, is in the sequence (see A016789).

Crossrefs

Cf. A016789, A020639, A104275.

Programs

Maple

A020639 := proc(n) if n = 1 then 1; else min(op(numtheory[factorset](n)) ) ; end if; end proc:
isA173977 := proc(n) A020639(2*n-1) < A020639(2*n-3) ; end proc:
for n from 2 to 400 do if isA173977(n) then printf("%d,",n) ; end if; end do: # R. J. Mathar, Mar 25 2010

Mathematica

lpf[n_] := lpf[n] = FactorInteger[n][[1, 1]]; Select[Range[2, 150], lpf[2*#-1] < lpf[2*#-3] &] (* Amiram Eldar, Oct 24 2024 *)

Extensions

More terms from R. J. Mathar, Mar 25 2010