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 A270268 For any prime consider the concatenation of its digits written in base b, and convert it to base 10: sequence lists primes that produce other primes for every base b, 3 <= b <= 9, under this process. 0
 1221221, 14201591, 39741391, 220290431, 554011061, 570264221, 623215031, 700648051, 705042731, 1021490321, 1046114051, 1107832991, 1136676421, 1192829461, 1221992311, 1362343261, 1712449621, 1723640701, 1724002061, 1773228511, 2122510631, 3008249821, 3120492691 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 1221992311 is the first prime that gives a prime for b = 2 too. LINKS EXAMPLE Digits of 39741391: in base 3 are 10, 100, 21, 11, 1, 10, 100, 1 and their concatenation is 1010021111101001 which is the prime 16090759 in base 10; in base 4 are 3, 21, 13, 10, 1, 3, 21, 1 and their concatenation is 321131013211 which is the prime 15061477 in base 10; in base 5 are 3, 14, 12, 4, 1, 3, 14, 1 and their concatenation is 31412413141 which is the prime 32935421 in base 10; in base 6 are 3, 13, 11, 4, 1, 3, 13, 1 and their concatenation is 31311413131 which is the prime 196874767 in base 10; in base 7 are 3, 12, 10, 4, 1, 3, 12, 1 and their concatenation is 31210413121 which is the prime 900203221 in base 10; in base 8 are 3, 11, 7, 4, 1, 3, 11, 1 and their concatenation is 3117413111 which is the prime 423499337 in base 10; in base 9 are 3, 10, 7, 4, 1, 3, 10, 1 and their concatenation is 3107413101 which is the prime 1209273301 in base 10. MAPLE P:= proc(q) local a, b, c, h, k, n, ok;  for n from 1 by 2 to q do if isprime(n) then ok:=1; for h from 3 to 9 do a:=[]; b:=n; for k from 1 to ilog10(n)+1 do c:=convert(b mod 10, base, h); if c=[] then c:=; fi; b:=trunc(b/10); a:=[op(a), op(c)]; od; a:=convert(a, base, h, 10); b:=0; for k from nops(a) by -1 to 1 do b:=b*10+a[k]; od; if not isprime(b) then ok:=0; break; fi; od; if ok=1 then print(n); fi; fi; od; end: P(10^12); CROSSREFS Cf. A000040. Sequence in context: A235910 A234997 A213703 * A257152 A257159 A254741 Adjacent sequences:  A270265 A270266 A270267 * A270269 A270270 A270271 KEYWORD nonn,base AUTHOR Paolo P. Lava, Mar 14 2016 STATUS approved

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Last modified January 27 17:36 EST 2022. Contains 350611 sequences. (Running on oeis4.)