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 A087631 Number of n-digit primes ending in 3 in base 10. 4
 1, 6, 35, 268, 2092, 17263, 146565, 1274244, 11272025, 101053126, 915743823, 8372470456, 77114448042 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA From Iain Fox, Aug 07 2018: (Start) a(n) ~ (1/4) * Integral_{x=10^(n-1)..10^n} (dx/log(x)). a(n) = A006879(n) - A087630(n) - A087632(n) - A087633(n), for n > 1. (End) EXAMPLE a(2) = 6, as there exist 6 two-digit prime numbers (13, 23, 43, 53, 73, and 83) with units place 3. a(3) = 35, since there are 35 three-digit numbers with units place digit as 3. MATHEMATICA Table[Length[Select[Range[10^n + 3, 10^(n + 1) - 7, 10], PrimeQ[#] &]], {n, 5}] (* Alonso del Arte, Apr 27 2014 *) PROG (Java) /** The terms of the sequences are generated by changing the range for j for the various numbers of digits. E.g., it ranges from 100 to 999 for three-digit numbers. */ float r, x; int c = 0, count = 0; for (float j = 100f; j < 1000f; j++) { for (float i = 2f; i < j; i++) { r = j % i; if (r == 0) c = 1; } if (c == 0) { x = j % 10; if (x == 3) count = count + 1; } c = 0; } System.out.println("count = " + count); (PARI) a(n) = my(c=0); forprime(p=10^(n-1), 10^n, if(p%10==3, c++)); c \\ Iain Fox, Aug 07 2018 CROSSREFS Cf. A006879, A073506, A087630, A087632, A087633. Sequence in context: A244267 A187443 A325115 * A167579 A357095 A030446 Adjacent sequences: A087628 A087629 A087630 * A087632 A087633 A087634 KEYWORD nonn,base,hard,more AUTHOR Meenakshi Srikanth (menakan_s(AT)yahoo.com) and Amarnath Murthy, Sep 15 2003 EXTENSIONS More terms from Ray Chandler, Oct 04 2003 Offset corrected by Iain Fox, Aug 07 2018 a(11) from Iain Fox, Aug 07 2018 a(12)-a(13) from Giovanni Resta, Aug 07 2018 STATUS approved

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Last modified March 24 19:29 EDT 2023. Contains 361510 sequences. (Running on oeis4.)