1,2

The first 10-digit palindrome in the decimal expansion of Pi (0136776310) first appears at a palindromic position (16061).

a(2) = 24 because the first 2-digit palindrome in the decimal expansion of Pi (33) starts 24 digits after the decimal point.

3.14159265358979323846264(33)...

With[{d = First@ RealDigits@ N[Pi, 10^6]}, Prepend[DeleteCases[Rest@ #, 0], First@ #] &@ Flatten@ Map[If[Length@ # == 0, 0, #[[1, 1]] - 1] &@ SequencePosition[d, #] &, Table[If[Length@ # == 0, {}, First@ #] &@ Select[Partition[d, n, 1], # == Reverse@ # &], {n, 20}]]] (* Michael De Vlieger, Jan 07 2017, Version 10.1 *)

(Python)

from sympy import S

# download https://stuff.mit.edu/afs/sipb/contrib/pi/pi-billion.txt, then

# with open('pi-billion.txt', 'r') as f: pi_digits = f.readline()

pi_digits = str(S.Pi.n(3*10**5+2))[:-2] # Alternative to above

pi_digits = pi_digits.replace(".", "")

def ispal(s): return s == s[::-1]

def a(n):

for idx in range(len(pi_digits)-n):

if ispal(pi_digits[idx:idx+n]):

return int(pi_digits[idx:idx+n]), idx

return None, None # Not found: Increase number of digits

print([a(n)[1] for n in range(1, 13)]) # Michael S. Branicky, Jan 10 2022

Cf. A000796, A002113, A279885.

Sequence in context: A040598 A097190 A103903 * A040599 A076721 A232988

Adjacent sequences: A280628 A280629 A280630 * A280632 A280633 A280634

nonn,base,more,less

Bobby Jacobs, Jan 06 2017

a(14)-a(15) from Michael De Vlieger, Jan 07 2017

a(16)-a(20) from Michael S. Branicky, Jan 10 2022

approved