A090543 - OEIS

A090543

a(1) = 3, then a(n) = least prime, not already present, beginning with the digit reversal of a(n-1).

3, 31, 13, 311, 113, 3119, 91139, 931193, 39113903, 30931193, 391139039, 930931193, 3911390393, 393093119329, 9239113903933, 3393093119329037, 7309239113903933023, 320339309311932903749, 94730923911390393302341

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..19.

EXAMPLE

a(3) = 13 because a(2) = 31 and the digit reversal of 31 is 13 which is prime.

a(4) = 311 because a(3) = 13, digit reversal of 13 is 31, which is already in the list. Smallest prime that starts with 31 is 311.

MAPLE

reverse := proc (nn) local n, m; m := 0; n := nn; while (n > 0) do m := m*10 + irem(n, 10, 'n'); od; m; end:

a := proc(n, m) option remember; global currSet; local currN, i, origN, j; if n = 0 then currSet := {m}; return m; end if; currN := reverse(a(n - 1, m)); if (not (evalb(currN in currSet))) then if (isprime(currN)) then currSet := currSet union {currN}; return currN; end if; end if; origN := currN; j := 1; while (true) do origN := 10 * origN; currN := origN; i := 0; while i < (10^j) do if (isprime(currN) and (not evalb(currN in currSet))) then currSet := currSet union {currN}; return currN; end if; currN := currN + 1; i := i + 1; end do; j := j + 1; end do; return currN; end proc; (Delgau)

CROSSREFS

Cf. A111463, A111462.

Sequence in context: A089281 A212729 A218357 * A215946 A139090 A238197

Adjacent sequences: A090540 A090541 A090542 * A090544 A090545 A090546

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Dec 09 2003; corrected Aug 04 2005

EXTENSIONS

More terms from Chris Deugau (deugaucj(AT)uvic.ca), Nov 07 2005

STATUS

approved