A049518 Starting index of a string of exactly 2 consecutive equal digits in the decimal expansion of Pi.

25, 35, 45, 60, 80, 95, 118, 126, 131, 136, 175, 183, 186, 202, 205, 212, 216, 218, 231, 258, 277, 283, 308, 310, 316, 318, 323, 361, 363, 365, 373, 378, 396, 402, 428, 438, 446, 454, 460, 473, 485, 495, 504, 508, 512, 517, 536, 560, 593, 622

Offset: 0

Author

Harvey P. Dale

Keywords

• nonn
• base

Comments

Digits 3,1,4,... are indexed 1,2,3,...

See A049514 for the variant "at least 2", which differs from a(11) on. - M. F. Hasler, Oct 18 2019

Examples

			From _M. F. Hasler_, Oct 18 2019: (Start)
The integer part of Pi*10^22 ends in 33, i.e., at position 22 starts the (first) string of two repeated digits 3, therefore a(1) = 22.
At position 154 starts a string of three '1's, so sequence A049514 lists both, 154 and 155, but this sequence lists none of these. (End)
		

Crossrefs

Cf. A049514-A049523.

Programs

Mathematica

Flatten[Position[Partition[RealDigits[Pi,10,1000][[1]],4,1],?(#[[1]] != #[[2]] && #[[2]]==#[[3]]&&#[[3]]!=#[[4]]&),1,Heads->False]]+1 (* _Harvey P. Dale, Jul 08 2017 *)

PARI

A049518_upto(N=999)={default(realprecision, N); my(p=digits(Pi\10^-N)); select(i->p[i]==p[i+1] && p[i]!=p[i-1] && p[i]!=p[i+2], [9..N-2])} \\ M. F. Hasler, Oct 18 2019