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Search: id:A090543
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| A090543 |
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a(1) = 3, then a(n) = least prime, not already present, beginning with the digit reversal of a(n-1). |
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3
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| 3, 31, 13, 311, 113, 3119, 91139, 931193, 39113903, 30931193, 391139039, 930931193, 3911390393, 393093119329, 9239113903933, 3393093119329037, 7309239113903933023, 320339309311932903749, 94730923911390393302341
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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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.
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MAPLE
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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)
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CROSSREFS
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Cf. A111463, A111462.
Sequence in context: A068698 A053300 A089281 this_sequence A139090 A042477 A023297
Adjacent sequences: A090540 A090541 A090542 this_sequence A090544 A090545 A090546
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KEYWORD
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base,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Dec 09 2003; corrected Aug 04 2005
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EXTENSIONS
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More terms from Chris Deugau (deugaucj(AT)uvic.ca), Nov 07 2005
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