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 A251360 Numbers n such that n is the concatenation of prime factors of pi(n), in increasing order. 2
 1117, 2163, 2537, 5137, 222926801 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Next term must be greater than 2*10^7. Numbers n such that n = A037276(A000720(n)). a(6) > 4.5*10^9. - Chai Wah Wu, Dec 11 2014 Conjecture: a(n) are numbers n such that n = A084317(A000720(n)). - Chai Wah Wu, Apr 04 2018 LINKS Table of n, a(n) for n=1..5. Chris Caldwell, G. L. Honaker and Lewis, 1117 EXAMPLE 1117 is in the sequence since pi(1117) = 11*17, 2163 is in the sequence since pi(2163) = 2*163, 2537 is in the sequence since pi(2537) = 2*5*37, and 5137 is in the sequence since pi(5137) = 5*137. MATHEMATICA a251360[n_Integer] := Select[Range[n], # == FromDigits[Flatten@IntegerDigits[First@ Transpose@ FactorInteger[PrimePi[#]]]] &]; a251360[10^5] (* Michael De Vlieger, Dec 03 2014 *) PROG (Python) from sympy import prime, factorint A251360_list, p = [], 3 for n in range(2, 10**6): ....q, fn = prime(n+1), factorint(n) ....m = int(''.join(str(d)*fn[d] for d in sorted(fn))) ....if p <= m < q: ........A251360_list.append(m) ....p = q # Chai Wah Wu, Dec 10 2014, corrected Apr 04 2018 CROSSREFS Cf. A000040, A000720, A251361, A251362. Sequence in context: A161848 A020380 A243527 * A201034 A264312 A145334 Adjacent sequences: A251357 A251358 A251359 * A251361 A251362 A251363 KEYWORD nonn,base,more AUTHOR Jahangeer Kholdi, Dec 01 2014 EXTENSIONS a(5) from Chai Wah Wu, Dec 10 2014 STATUS approved

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Last modified May 26 21:09 EDT 2024. Contains 372844 sequences. (Running on oeis4.)