A078604 - OEIS

%I #31 Mar 02 2019 02:50:11

%S 3,31,157,349,103,314159,392699,8263,7853,9786893,28954771,

%T 157079632679,68246533,4304347,67649047,1002742628021,1170899,

%U 990371647,14523877,1186001,1023100457,451661057,1492315939,381315143078063,950007203269

%N Largest prime factor of the integer formed by truncating the decimal expansion of Pi to n places.

%H Robert G. Wilson v, <a href="/A078604/b078604.txt">Table of n, a(n) for n = 0..169</a> (first 101 terms from Ryan Moore)

%H I. O. Angell, and H. J. Godwin, <a href="http://dx.doi.org/10.1090/S0025-5718-1977-0427213-2">On Truncatable Primes</a> Math. Comput. 31, 265-267, 1977.

%H Hisanori Mishima, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/matha1/de_pi000.htm"> Decimal expansions of π (n = 0 to 100)</a>

%H Hisanori Mishima, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/matha1/de_pi100.htm"> Decimal expansions of π (n = 101 to 200)</a>

%H Hisanori Mishima, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/matha1/de_pi200.htm"> Decimal expansions of π (n = 201 to 250)</a>

%H <a href="/index/Tri#tprime">Index entries for sequences related to truncatable primes</a>

%F a(n) = A006530(A011545(n)). - _Michel Marcus_, Dec 28 2013

%F a(n) = A011545(n) iff n is a term in A060421. - _Robert G. Wilson v_, May 30 2015

%e a(3) = 157 since 314 = 2*157.

%t f[n_] := FactorInteger[ IntegerPart[ Pi*10^(n - 1)]][[-1, 1]]; Array[f, 23] (* _Robert G. Wilson v_, May 30 2015 *)

%o (PARI) a(n) = vecmax(factor(floor(Pi*10^n))[, 1]); \\ _Michel Marcus_, Dec 28 2013

%Y Cf. A011545, A006530.

%Y Cf. A089281.

%K nonn,base

%O 0,1

%A _Jason Earls_, Dec 09 2002

%E More terms from _Ryan Moore_, Dec 28 2013