The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A245571 a(n) is the smallest prime number with at least two digits formed by the concatenation of the subsequent digits of Pi, starting at the n-th digit, ignoring the decimal point. 1
 31, 14159, 41, 1592653, 59, 9265358979323, 26535897932384626433832795028841971693993751058209, 653, 53, 35897, 5897, 89, 97, 79, 9323, 32384626433832795028841971693993751058209749445923078164062862089986280348253421, 23, 38462643383 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(19) has 3057 digits. - Robert Israel, Aug 27 2014 a(20) = 462643. - Felix Fröhlich, Aug 30 2014 a(21) has >= 3490 digits, a(22) = 2643383, a(22)-a(42) have 20 or fewer digits. - Chai Wah Wu, Sep 24 2014 LINKS EXAMPLE a(4) = 1592653, because starting at the 4th digit in the expansion, the smallest substring of the digits of Pi forming a prime number is 3.14|1592653|589... MAPLE N:= 1000: # to use up to N+1 digits of pi. nmax:= 30: # to get up to a(nmax), if possible. S:= floor(10^N*Pi): L:= ListTools:-Reverse(convert(S, base, 10)): for n from 1 to nmax do   p:= L[n];   for k1 from n+1 to N+1 do     p:= 10*p + L[k1];     if isprime(p) then break fi   od:   if k1 > N+1 then     A[n]:= "Ran out of digits";     break    else     A[n]:= p   end od: seq(A[i], i=1..n-1); # Robert Israel, Aug 27 2014 PROG (Python) from sympy.mpmath import * from sympy import isprime def A245571(n): ....mp.dps = 1000+n ....s = nstr(pi, mp.dps)[:-1].replace('.', '')[n-1:] ....for i in range(len(s)-1): ........p = int(s[:i+2]) ........if p > 10 and isprime(p): ............return p ....else: ........return 'Ran out of digits' # Chai Wah Wu, Sep 16 2014, corrected Chai Wah Wu, Sep 24 2014 CROSSREFS Cf. A000796, A005042, A047777, A076094, A104841, A195834, A198018, A198019, A198187. Sequence in context: A261947 A069451 A073099 * A074218 A161395 A215610 Adjacent sequences:  A245568 A245569 A245570 * A245572 A245573 A245574 KEYWORD nonn,base AUTHOR Felix Fröhlich, Aug 22 2014 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 16 23:53 EDT 2021. Contains 347477 sequences. (Running on oeis4.)