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A089749 a(n) = smallest m > a(n-1) such that concatenation nm is a prime. 2
1, 3, 7, 19, 21, 31, 33, 39, 41, 49, 51, 59, 61, 71, 79, 93, 107, 119, 121, 123, 139, 147, 159, 169, 171, 177, 179, 181, 191, 197, 219, 233, 247, 253, 257, 263, 273, 281, 293, 343, 351, 359, 391, 417, 427, 439, 441, 449, 451, 459, 461, 489, 503, 517, 529, 531 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Up to a(10^6), a(n) =~ 100000 + 24n + 10^(-6*n), which is almost a straight line. - Robert G. Wilson v

LINKS

Table of n, a(n) for n=1..56.

EXAMPLE

a(5) = 21 because the first prime after a(4) = 419 beginning with 5 is 521.

MATHEMATICA

a[1] = 1; a[1] = 1; a[n_] := a[n] = Block[{k = IntegerDigits[n], l = a[n - 1] + 2}, While[ !PrimeQ[ FromDigits[ Join[k, IntegerDigits[l]]]], l += 2]; l]; Table[ a[n], {n, 1, 55}]

CROSSREFS

Sequence in context: A151858 A242170 A032675 * A032667 A109991 A248219

Adjacent sequences:  A089746 A089747 A089748 * A089750 A089751 A089752

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Nov 20 2003

EXTENSIONS

Corrected and extended by Robert G. Wilson v, Dec 05 2003

STATUS

approved

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Last modified October 21 14:20 EDT 2019. Contains 328301 sequences. (Running on oeis4.)