A202025 - OEIS

A202025

Position of second appearance of set of first n terms in the sequence of odd primes modulo 4.

3, 4, 8, 16, 16, 19, 60, 221, 654, 654, 654, 654, 654, 30291, 30291, 30291, 30291, 250231, 342916, 342916, 472727, 1934365, 1934365, 11877702, 11877702, 11877702

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OFFSET

1,1

COMMENTS

Next term, a(27) > 3*10^7.

LINKS

Table of n, a(n) for n=1..26.

EXAMPLE

Consider the sequence of odd primes modulo 4: S= 3, 1, 3, 3, 1, 1, 3, 3, 1, 3, 1, 1, 3, 3, 1, 3, 1,... . Then

a(1)=3 because 2nd appearance of 3 is S(3),

a(2)=4 because 2nd appearance of (3,1) begins at S(4),

a(3)=8 because 2nd appearance of (3,1,3) begins at S(8),

a(4)=16 because 2nd appearance of (3,1,3,3) begins at S(16).

MATHEMATICA

nn=3*10^7; s=Table[Mod[Prime[n], 4], {n, 2, nn}]; Reap[k1=2; Do[tn=Take[s, n]; Do[If[tn==Take[s, {k, k+n-1}], Sow[k]; k1=k; Break[]], {k, k1, nn-n-1}], {n, 26}]][[2, 1]]

CROSSREFS

Cf. A039702.

Sequence in context: A027977 A165438 A293781 * A227615 A049894 A198633

Adjacent sequences: A202022 A202023 A202024 * A202026 A202027 A202028

KEYWORD

nonn

AUTHOR

Zak Seidov, Dec 09 2011

STATUS

approved