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A307328 Indices of prime Ulam numbers: numbers k such that A002858(k) is prime. 3
2, 3, 7, 8, 15, 17, 25, 31, 41, 48, 69, 73, 91, 97, 106, 107, 123, 125, 138, 167, 172, 177, 181, 193, 194, 241, 242, 246, 267, 280, 286, 287, 297, 306, 312, 322, 323, 338, 340, 343, 353, 354, 382, 388, 393, 398, 403, 411, 412, 415, 416, 433, 444, 448, 460 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..1000

FORMULA

A002858(a(n)) = A068820(n).

MATHEMATICA

ulams = {1, 2}; Do[AppendTo[ulams, n = Last[ulams]; While[n++; Length[ DeleteCases[Intersection[ulams, n - ulams], n/2, 1, 1]] != 2]; n], {100}]; Flatten[Position[ulams, _?(PrimeQ[#] &)]] (* after Jean-Fran├žois Alcover at A002858 *)

CROSSREFS

Cf. A002858, A068820.

Sequence in context: A084406 A075648 A071527 * A097095 A101755 A076550

Adjacent sequences:  A307325 A307326 A307327 * A307329 A307330 A307331

KEYWORD

nonn

AUTHOR

Amiram Eldar, Apr 02 2019

STATUS

approved

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Last modified January 27 12:01 EST 2020. Contains 331295 sequences. (Running on oeis4.)