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 A077716 a(1) = 19; thereafter a(n) = the smallest prime of the form d0...0a(n-1), where d is a single digit, or 0 if no such prime exists. 4
 19, 419, 5419, 35419, 435419, 80435419, 30000080435419, 1030000080435419, 91030000080435419, 20091030000080435419, 720091030000080435419, 50720091030000080435419, 650720091030000080435419, 10650720091030000080435419, 2000000010650720091030000080435419 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n) is the smallest prime obtained by prefixing a(n-1) with a number of the form d*10^k where d is a single digit, 0 < d < 10, and k >= 0. Conjecture: d*10^k always exists. LINKS Michael S. Branicky, Table of n, a(n) for n = 1..51 MAPLE a:= proc(n) option remember; local k, m, d, p; if n=1 then 19 else k:= a(n-1); for m from length(k) do for d to 9 do p:= k +d*10^m; if isprime(p) then return p fi od od fi end: seq(a(n), n=1..20); # Alois P. Heinz, Jan 12 2015 PROG (Python) from sympy import isprime from itertools import islice def agen(an=19): while True: yield an pow10 = 10**len(str(an)) while True: found = False for t in range(pow10+an, 10*pow10+an, pow10): if isprime(t): an = t; found = True; break if found: break pow10 *= 10 print(list(islice(agen(), 15))) # Michael S. Branicky, Jun 23 2022 CROSSREFS Cf. A069612, A077713, A077714, A077715. Sequence in context: A202040 A244765 A069612 * A089573 A284332 A121938 Adjacent sequences: A077713 A077714 A077715 * A077717 A077718 A077719 KEYWORD base,nonn AUTHOR Amarnath Murthy, Nov 19 2002 EXTENSIONS More terms from Ray Chandler, Jul 23 2003 Definition clarified by N. J. A. Sloane, Jan 19 2015 STATUS approved

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Last modified November 27 07:59 EST 2022. Contains 358362 sequences. (Running on oeis4.)