A251239 Indices of prime numbers in A098550.

2, 3, 9, 15, 22, 23, 30, 43, 51, 61, 62, 79, 87, 88, 101, 114, 127, 132, 142, 153, 158, 167, 175, 194, 204, 215, 222, 233, 238, 247, 274, 283, 296, 301, 324, 329, 338, 355, 364, 375, 386, 393, 414, 423, 430, 435, 452, 479, 490, 497, 506, 523, 528, 541, 550

Offset: 1

Author

Reinhard Zumkeller, Dec 02 2014

Keywords

• nonn

Comments

It is conjectured that every prime appears in A098550, and if so then A098550(a(n)) = A000040(n). [Comment edited by N. J. A. Sloane, Dec 15 2014] [It is now known that every prime appears in A098550, although it is not known that they appear in their right order. - N. J. A. Sloane, Dec 25 2014]

A010051(A098550(a(n))) = 1; A049084(A098550(a(n))) > 0.

Conjecture: a(n) = A251541(n) + 2 for n > 4. - Reinhard Zumkeller, Dec 16 2014

A253049(n) = A098550(a(n)+1). - Reinhard Zumkeller, Dec 29 2014

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A098550, A010051, A049084, A251392, A247253 (first differences), A251595, A251541, A253049, A253048.

This is a subsequence of A251391 and A251241,

Programs

Haskell

a251239 n = a251239_list !! (n-1)
a251239_list = filter ((== 1) . a010051' . a098550) [1..]

Mathematica

a098550[lst_List] :=
Block[{k = 4},
  While[GCD[lst[[-2]], k] == 1 || GCD[lst[[-1]], k] > 1 ||
    MemberQ[lst, k], k++]; Append[lst, k]];
a251239[n_] :=
Flatten@Position[Nest[a098550, {1, 2, 3}, n], Integer?PrimeQ]; a251239[550] (* _Michael De Vlieger, Dec 23 2014, based on Robert G. Wilson v at A098550 *)