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A251239 Indices of prime numbers in A098550. 15
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

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

MATHEMATICA

a098850[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[a098850, {1, 2, 3}, n], _Integer?PrimeQ]; a251239[550] (* Michael De Vlieger, Dec 23 2014, based on Robert G. Wilson v at A098850 *)

PROG

(Haskell)

a251239 n = a251239_list !! (n-1)

a251239_list = filter ((== 1) . a010051' . a098550) [1..]

CROSSREFS

Cf. A098550, A000040, A010051, A049084, subsequence of A251391 and A251241, A247253 (first differences).

Cf. A098550, A000040, A010051, A049084, A251392, subsequence of A251391 and A251241, A247253 (first differences), A251595.

Cf. A251541.

Cf. A253049, A253048.

Sequence in context: A091361 A092352 A061933 * A124881 A054416 A291868

Adjacent sequences:  A251236 A251237 A251238 * A251240 A251241 A251242

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Dec 02 2014

STATUS

approved

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Last modified June 2 18:09 EDT 2020. Contains 334787 sequences. (Running on oeis4.)