A133782 Indices of monotonically increasing primes which centrally enclose the prime sequence in A133781.

31, 32, 36, 40, 187, 321, 327, 452, 580, 590, 821, 831, 940, 942, 946, 955, 965, 1186, 1194, 1198, 1200, 1208, 1213, 419, 429, 2362, 2367, 3348, 3350, 3353, 3372, 3375, 3381, 3383, 4339, 4341, 4347, 5284, 5288, 7995, 8000, 8001, 8009, 8011, 8016, 8887

Offset: 1

Author

Enoch Haga, Sep 23 2007

Keywords

• easy
• nonn
• uned

Comments

A break occurs at index 1213 of 9833 and 89 must be centrally located at index 419 prime 2897 and the monotonic sequence resumed from that point onward until the next break occurs

Examples

			a(23) is the index 1213 of prime 9833 where the prime 83 is centrally located.
		

Crossrefs

Cf. A133781 A075595.

Programs

UBASIC

10 C=26:Q=str(C):T=443 20 'monotonically increasing primes 30 'centered in primes 40 'change val(m) in 100 50 'adjust T in line 10 after every break 60 N=101 70 A=3:S=sqrt(N) 80 B=N\A 90 if B*A=N then N=N+2:goto 70 100 A=A+2 110 if A<=sqrt(N) then 80 120 Z=str(N):W=alen(N):W=W-2:M=mid(Z,3,W): if M=Q then print C,N:stop 130 if val(M)=nxtprm(T) then print Q,M,Z:T=val(M):stop 140 C=C+1:Q=str(C) 150 N=N+2:goto 70

Formula

Centrally enclose the prime sequence in another montotonically increasing prime sequence (if a break occurs begin over at that point)