A078604 Largest prime factor of the integer formed by truncating the decimal expansion of Pi to n places.

3, 31, 157, 349, 103, 314159, 392699, 8263, 7853, 9786893, 28954771, 157079632679, 68246533, 4304347, 67649047, 1002742628021, 1170899, 990371647, 14523877, 1186001, 1023100457, 451661057, 1492315939, 381315143078063, 950007203269

Offset: 0

Author

Jason Earls, Dec 09 2002

Keywords

• nonn
• base

Examples

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

Links

• Tyler Busby, Table of n, a(n) for n = 0..200 (terms 0..100 from Ryan Moore, terms 101..169 from Robert G. Wilson)
• I. O. Angell, and H. J. Godwin, On Truncatable Primes Math. Comput. 31, 265-267, 1977.
• Hisanori Mishima, Decimal expansions of π (n = 0 to 100)
• Hisanori Mishima, Decimal expansions of π (n = 101 to 200)
• Hisanori Mishima, Decimal expansions of π (n = 201 to 250)
• Index entries for sequences related to truncatable primes

Crossrefs

Cf. A011545, A006530.

Cf. A089281.

Programs

Mathematica

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

PARI

a(n) = vecmax(factor(floor(Pi*10^n))[, 1]); \\ Michel Marcus, Dec 28 2013

Formula

a(n) = A006530(A011545(n)). - Michel Marcus, Dec 28 2013

a(n) = A011545(n) iff n is a term in A060421. - Robert G. Wilson v, May 30 2015

Extensions

More terms from Ryan Moore, Dec 28 2013