1,1

The first 184 resp. 300 terms of A081430 allow us to deduce 44 resp. 84 consecutive terms of this sequence. - M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Apr 05 2007

R. K. Guy, Unsolved Problems in Number Theory, A18.

M. F. Hasler, Table of n, a(n) for n=1..282

{ a(n) } = { p = 2*m*A081430(k)+1 | k=1,2,...,oo and m=1,2,... such that p is prime and m has no factor of class > 11- } - M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Apr 05 2007

a(1) = 14920303 = 1+2*A081430(3)*3 is the smallest 12- prime

PrimeFactors[n_Integer] := Flatten[ Table[ #[[1]], {1}] & /@ FactorInteger[n]]; f[n_Integer] := Block[{m = n}, If[m == 0, m = 1, While[ IntegerQ[m/2], m /= 2]; While[ IntegerQ[m/3], m /= 3]]; Apply[Times, PrimeFactors[m] - 1]]; ClassMinusNbr[n_] := Length[ NestWhileList[f, n, UnsameQ, All]] - 3; Prime[ Select[ Range[3610000], ClassMinusNbr[ Prime[ # ]] == 12 &]]

(PARI) nextclassminus( a, p=1, n=[] )={ while( p, n=concat(n, p); p=0; for( i=1, #a, if( p & 2*a[i] >= p-1, break); for( k=ceil(n[ #n]/2/a[i]), a[ #a]/a[i], if( p & 2*k*a[i] >= p-1, break); if( isprime(2*k*a[i]+1), p=2*k*a[i]+1; break(1+(k==1)); )))); vecextract(n, "^1")}; A081640 = nextclassminus(A081430) - M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Apr 05 2007

Cf. A005113, A005105, A005106, A005107, A005108, A081633, A081633, A081635, A081636, A081637, A081638.

Cf. A056637, A081430, A081641.

Sequence in context: A111346 A136608 A015364 this_sequence A157418 A125565 A104334

Adjacent sequences: A081637 A081638 A081639 this_sequence A081641 A081642 A081643

nonn

Robert G. Wilson v (rgwv(AT)rgwv.com), Mar 23 2003

Edited by N. J. A. Sloane (njas(AT)research.att.com) at the suggestion of Andrew Plewe, May 21 2007