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 A241007 Decimal encoding of the prime factorization of a(n) is a prime. 1
 3, 6, 7, 8, 13, 19, 20, 31, 35, 38, 40, 43, 44, 45, 56, 60, 63, 65, 68, 69, 96, 97, 103, 104, 109, 116, 119, 122, 125, 133, 138, 151, 157, 159, 160, 171, 174, 181, 189, 193, 204, 209, 211, 212, 215, 216, 220, 221, 232, 241, 248, 250, 254, 267, 271, 273, 280 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This sequence gives all arguments for which A067599 is prime: A067599(a(n)) = prime. - Wolfdieter Lang, Aug 16 2014 LINKS Paolo P. Lava, Table of n, a(n) for n = 1..1000 FORMULA Sequence of the members of the set {k >= 2: A067599(k) is a prime} in increasing order. - Wolfdieter Lang, Aug 16 2014 EXAMPLE Prime factorization of a(4) = 8 is 2^3 and its decimal encoding is A067599(8) = 23 that is prime. Prime factorization of a(188) = 994 is 2^1*7^1*71^1 and its decimal encoding is A067599(994) = 2171711 that is prime. MAPLE with(numtheory); P:=proc(q) local a, b, c, d, k, j, n; for n from 1 to q do a:=(ifactors(n)[2]); b:=[]; for k from 1 to nops(a) do b:=[op(b), a[k, 1]]; od; b:=sort(b); c:=0; for k from 1 to nops(b) do d:=1; while b[k]<>a[d, 1] do d:=d+1; od; j:=b[k]*10^(ilog10(a[d, 2])+1)+a[d, 2]; c:=c*10^(ilog10(j)+1)+j; od; if isprime(c) then print(n); fi; od; end: P(1000); CROSSREFS Cf. A067598, A067599. Sequence in context: A293758 A222305 A189098 * A139451 A081291 A189095 Adjacent sequences: A241004 A241005 A241006 * A241008 A241009 A241010 KEYWORD nonn,easy,base AUTHOR Paolo P. Lava, Aug 07 2014 EXTENSIONS Edited: Name n-> a(n), cf. A067599, examples specified. - Wolfdieter Lang, Aug 16 2014 STATUS approved

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Last modified February 28 08:11 EST 2024. Contains 370393 sequences. (Running on oeis4.)