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%I #11 Sep 29 2015 00:47:42
%S 109,1091,109174406370390610145415947333,
%T 10917440637039061014541594733338923249860501214082473450059137
%N Primes formed by the initial digits of the decimal expansion of 1/Catalan's constant.
%C Primes found in 1/ A006752.
%C a(5) = 109174406...792972361 has 109 digits,
%C a(6) = 109174406...955798301 has 271 digits,
%C a(7) = 109174406...813410233 has 319 digits,
%C a(8) = 109174406...519744361 has 1223 digits.
%e 1/Catalan's constant = 1.09174406..., so a(1) = 109 ; a(2) = 1091.
%p Digits := 100; n0 := evalf(1/Catalan); for i from 1 to 100 do x := trunc(10^i*n0):
%p if isprime(x) then printf(`%d, `, x): fi: od:
%o (PARI) default(realprecision,350); C=intnum(t=0,1,atan(t)/t); for(k=1,default(realprecision),ispseudoprime(10^k\C) && print(10^k\C," digits: ",k+1)) \\ _M. F. Hasler_, Nov 24 2010
%Y Cf. A006752, A014538.
%K nonn,base
%O 1,1
%A _Michel Lagneau_, Nov 24 2010