A387634 Indices k such that s(k) is a prime p, s(k-1) = 2*p, and s(k+1) = 3*p, where s = A386482.

5, 11, 24, 31, 57, 76, 236, 479, 1532, 7652, 82123, 129791, 274542, 419569, 3367328, 7002435, 7690249, 45355072

Offset: 1

Author

Michael De Vlieger, Sep 04 2025

Keywords

• nonn
• more
• new

Examples

			Table of n, a(n), with a(n) = k, listing s(k) and its immediate neighbors:
 n  a(n) = k     s(k-1)      s(k)     s(k+1)
--------------------------------------------
 1         5         6         3          9
 2        11        14         7         21
 3        24        22        11         33
 4        31        38        19         57
 5        57        62        31         93
 6        76        94        47        141
 7       236       262       131        393
 8       479       634       317        951
 9      1532      1894       947       2841
10      7652      8654      4327      12981
11     82123     96182     48091     144273
12    129791    154474     77237     231711
13    274542    316978    158489     475467
14    419569    475466    237733     713199
15   3367328   3946174   1973087    5919261
16   7002435   6796442   3398221   10194663
17   7690249   8819038   4409519   13228557
		

Crossrefs

Cf. A064413, A386482, A386483, A387072, A387076, A387077, A387522, A387523, A387524.

Programs

Mathematica

s = Import["https://oeis.org/A386482/b386482.txt", "Data"][[All, -1]]; m = Length[s]; t = TakeWhile[Import["https://oeis.org/A387077/b387077.txt", "Data"][[All, -1]], # <= m &]; Select[t, #1 == 2 #2 && #3 == 3 #2 & @@ s[[# - 1 ;; # + 1]] &] ]

Extensions

a(18) from Chai Wah Wu, Sep 06 2025