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A053600
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a(1) = 2; for n>=1, a(n+1) is the smallest palindromic prime with a(n) as a central substring.
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10
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2, 727, 37273, 333727333, 93337273339, 309333727333903, 1830933372733390381, 92183093337273339038129, 3921830933372733390381293, 1333921830933372733390381293331, 18133392183093337273339038129333181
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OFFSET
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1,1
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REFERENCES
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G. L. Honaker, Jr. and Chris K. Caldwell, Palindromic Prime Pyramids, J. Recreational Mathematics, Vol. 30(3) 169-176, 1999-2000.
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LINKS
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Clark Kimberling, Table of n, a(n) for n = 1..200
P. De Geest, Palindromic Prime Pyramid Puzzle by G.L.Honaker,Jr
G. L. Honaker, Jr. and Chris Caldwell, Prime Curios! 18133...33181 (35-digits)
G. L. Honaker, Jr. & C. K. Caldwell, Palindromic Prime Pyramids
G. L. Honaker, Jr. & C. K. Caldwell, Supplement to "Palindromic Prime Pyramids"
Ivars Peterson, Primes, Palindromes, and Pyramids, Science News.
Inder J. Taneja, Palindromic Prime Embedded Trees, RGMIA Res. Rep. Coll. 20 (2017), Art. 124.
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EXAMPLE
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As a triangle:
.........2
........727
.......37273
.....333727333
....93337273339
..309333727333903
1830933372733390381
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MATHEMATICA
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d[n_] := IntegerDigits[n]; t = {x = 2}; Do[i = 1; While[! PrimeQ[y = FromDigits[Flatten[{z = d[i], d[x], Reverse[z]}]]], i++]; AppendTo[t, x = y], {n, 10}]; t (* Jayanta Basu, Jun 24 2013 *)
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PROG
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(Python)
from gmpy2 import digits, mpz, is_prime
A053600_list, p = [2], 2
for _ in range(30):
....m, ps = 1, digits(p)
....s = mpz('1'+ps+'1')
....while not is_prime(s):
........m += 1
........ms = digits(m)
........s = mpz(ms+ps+ms[::-1])
....p = s
....A053600_list.append(int(p)) # Chai Wah Wu, Apr 09 2015
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CROSSREFS
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Cf. A000040, A002385, A047076, A052205, A034276, A256957, A052091, A052092, A261881.
Sequence in context: A062066 A174368 A082621 * A090275 A090565 A072384
Adjacent sequences: A053597 A053598 A053599 * A053601 A053602 A053603
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KEYWORD
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base,nonn
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AUTHOR
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G. L. Honaker, Jr., Jan 20 2000
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STATUS
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approved
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