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 A087630 Number of n-digit primes ending in 1 in base 10. 4
 0, 5, 35, 266, 2081, 17230, 146487, 1274194, 11271088, 101050133, 915755611, 8372443850, 77114409020 (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) - A087631(n) - A087632(n) - A087633(n), for n > 1. (End) EXAMPLE a(2) = 5 as there exist 5 two-digit prime numbers (11, 31, 41, 61, and 71) with units place 1. a(3) = 35, since there are 35 three-digit numbers with units place digit as 1. MATHEMATICA Table[Length[Select[Range[10^n + 1, 10^(n + 1) - 9, 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 == 1) 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==1, c++)); c \\ Iain Fox, Aug 07 2018 CROSSREFS Cf. A006879, A073505, A087631, A087632, A087633. Sequence in context: A104532 A292839 A180900 * A084135 A229111 A138233 Adjacent sequences:  A087627 A087628 A087629 * A087631 A087632 A087633 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 December 13 06:26 EST 2019. Contains 329968 sequences. (Running on oeis4.)