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 A322160 Fermat pseudoprimes to base 2 that are octadecagonal. 2
 8481, 14491, 29341, 62745, 196093, 396271, 526593, 2184571, 2513841, 5256091, 7017193, 8137585, 13448593, 15247621, 16053193, 16879501, 18740971, 20494401, 29878381, 33704101, 35703361, 36724591, 41607721, 42709591, 69741001, 70593931, 80927821, 82976181 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Rotkiewicz proved that under Schinzel's Hypothesis H this sequence is infinite. Intersection of A001567 and A051870. The corresponding indices of the octadecagonal numbers are 33, 43, 61, 89, 157, 223, 257, 523, 561, 811, 937, 1009, 1297, 1381, 1417, 1453, 1531, ... LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 Andrzej Rotkiewicz, On some problems of W. Sierpinski, Acta Arithmetica, Vol. 21 (1972), pp. 251-259. Wikipedia, Schinzel's Hypothesis H. MATHEMATICA octadec[n_]:=n(8n-7); Select[octadec[Range[1, 1000]], PowerMod[2, (# - 1), #]==1 &] PROG (PARI) isok(n) = (n>1) && ispolygonal(n, 18) && !isprime(n) && (Mod(2, n)^n==2); \\ Michel Marcus, Nov 29 2018 CROSSREFS Cf. A001567, A051870, A293623, A293624, A322161. Sequence in context: A232907 A151643 A031590 * A253499 A253492 A253453 Adjacent sequences:  A322157 A322158 A322159 * A322161 A322162 A322163 KEYWORD nonn AUTHOR Amiram Eldar, Nov 29 2018 STATUS approved

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Last modified June 18 09:17 EDT 2021. Contains 345098 sequences. (Running on oeis4.)