A156604 a(1)=2; for n > 0, a(n+1) is the smallest prime of A046704 larger than a(n) such that the sequence of digit sums of a(n) is nondecreasing.

2, 3, 5, 7, 29, 47, 67, 89, 179, 197, 199, 379, 397, 487, 577, 599, 797, 887, 977, 1499, 1697, 1787, 1877, 1949, 2399, 2579, 2687, 2777, 2939, 2957, 2999, 3989, 4799, 4889, 4999, 6997, 7699, 7789, 7879, 8599, 8689, 8779, 8887, 9679, 9697, 9769, 9787, 9859

Offset

1,1

Comments

The slowest increasing sequence that is a subsequence of A046704 such that the sequence of A007953(a(n)) is nondecreasing. - R. J. Mathar, Mar 29 2010

Links

Table of n, a(n) for n=1..48.

Example

The first several terms after a(1)=2 are
    3 (3 > 2);
    5 (5 > 3);
    7 (7 > 5);
   29 (2 + 9 > 7);
   47 (4 + 7 = 2 + 9);
   67 (6 + 7 > 4 + 9);
   89 (8 + 9 > 6 + 7);
  179 (1 + 7 + 9 = 8 + 9);
  197 (1 + 9 + 7 = 8 + 9).

Maple

A007953 := proc(n) local d ; add(d, d= convert(n, base, 10)) ; end proc:
isA046704 := proc(n) isprime(n) and isprime(A007953(n)) ; end proc:
A156604 := proc(n) option remember ; local psprev, i ; if n = 1 then 2 ; else psprev := A007953(procname(n-1)) ; for i from procname(n-1)+1 do if isA046704(i) then if A007953(i) >= psprev then return i ; end if; end if; end do: end if ; end proc:
seq(A156604(n), n=1..80) ; # R. J. Mathar, Mar 18 2010
From R. J. Mathar, Mar 29 2010: (Start)
A007953 := proc(n) add(d, d= convert(n, base, 10)) ; end proc:
isA028834 := proc(n) local d; add(d, d= convert(n, base, 10)) ; isprime(%) ; end proc:
isA046704 := proc(n) isprime(n) and isA028834(n) ; end proc:
A156604 := proc(n) option remember; if n = 1 then 2; else for a from procname(n-1)+1 do if isA046704(a) and A007953(a) >= A007953(procname(n-1)) then return a; end if; end do: end if; end proc: seq(A156604(n), n=1..100) ; (End)

Crossrefs

Cf. A000040, A007953, A067954.

Sequence in context: A091924 A358382 A069108 * A046864 A090712 A082257

Adjacent sequences: A156601 A156602 A156603 * A156605 A156606 A156607

Keyword

nonn,base

Author

Juri-Stepan Gerasimov, Feb 11 2009

Extensions

Definition, terms and examples corrected by R. J. Mathar, Mar 18 2010

179 and 1877 inserted, and 9 terms after 4889 replaced with the single term 4999, by R. J. Mathar, Mar 29 2010

Status

approved