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 A341017 Primes p such that placing digit i at both ends of p produces another prime for at least two of i = [1,3,7, 9]. 1
 2, 5, 17, 23, 29, 31, 41, 43, 47, 53, 61, 67, 71, 73, 83, 101, 107, 113, 131, 149, 197, 239, 241, 257, 263, 269, 293, 317, 347, 359, 389, 401, 421, 431, 443, 503, 521, 557, 593, 599, 607, 641, 647, 677, 683, 701, 757, 797, 827, 887, 911, 953, 1031, 1103, 1109, 1117, 1171, 1181, 1187, 1223, 1277 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers that are in at least two of A069687, A069688, A069689 and A069690. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE a(3) = 17 is a term because 17 is in A069687 and A069689, i.e. 1171 and 7177 are prime. MAPLE filter:= proc(n) local i; isprime(n) and numboccur(true, [seq(isprime(i+10*n+i*10^(2+ilog10(n))), i=[1, 3, 7, 9])]) >= 2 end proc: select(filter, [2, seq(i, i=3..1000)]); PROG (Python) from sympy import isprime, nextprime def ok(p): return sum(isprime(int(c+str(p)+c)) for c in "1379") >= 2 def aupto(limit): # only test primes alst, p = [], 2 while p <= limit: if ok(p): alst.append(p) p = nextprime(p) return alst print(aupto(1277)) #Michael S. Branicky, Feb 02 2021 CROSSREFS Cf. A069687, A069688, A069689, A069690. Sequence in context: A215273 A041283 A042049 * A069689 A307479 A106021 Adjacent sequences: A341014 A341015 A341016 * A341018 A341019 A341020 KEYWORD nonn,base AUTHOR J. M. Bergot and Robert Israel, Feb 02 2021 STATUS approved

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Last modified February 23 15:29 EST 2024. Contains 370283 sequences. (Running on oeis4.)