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 A271438 Numbers n such that the number formed by concatenating in ascending order the first n multidigit palindromic primes is prime. 0
 1, 17, 451 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS G. L. Honaker, Jr. and C. Caldwell, 11101...10301 (52-digits), Prime Curios!. EXAMPLE Concatenating in ascending order the 17 smallest palindromic primes with at least two digits gives 1110113115118119131335337338372775778779791992910301, which is prime, so 17 is a term of the sequence. PROG (PARI) nextpalprime(n) = my(p=nextprime(n)); while(p!=eval(concat(Vecrev(Str(p)))), p=nextprime(p+1)); p terms(n) = my(i=0, k=1, s="", p=10); while(i < n, p=nextpalprime(p+1); s=Str(s, p); if(ispseudoprime(eval(s)), print1(k, ", "); i++); k++) terms(3) \\ print initial three terms (Python) from sympy import isprime, nextprime def ispal(n): strn = str(n); return strn == strn[::-1] def agen():   np, p, pstr = 1, 11, "11"   while True:     if isprime(int(pstr)): yield np     p = nextprime(p)     while not ispal(p): p = nextprime(p)     np += 1     pstr += str(p) for an in agen(): print(an, end=", ") # Michael S. Branicky, Jan 17 2021 CROSSREFS Cf. A002385. Sequence in context: A301642 A035022 A012117 * A122430 A009051 A035276 Adjacent sequences:  A271435 A271436 A271437 * A271439 A271440 A271441 KEYWORD nonn,base,more,bref AUTHOR Felix FrÃ¶hlich, Apr 07 2016 STATUS approved

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Last modified January 22 12:12 EST 2022. Contains 350481 sequences. (Running on oeis4.)