A251361 Numbers n such that pi(n) is the concatenation of distinct prime factors of n, in decreasing order.

4, 100, 31509, 7560625

Offset

1,1

Comments

Next term must be greater than 4*10^8.

Numbers n such that A000720(n) = A084317(n). - Michel Marcus, Dec 06 2014.

Links

Table of n, a(n) for n=1..4.

Example

4 is in the sequence since 4=2^2 and pi(4)=2,
100 is in the sequence since 100=2^2*5^2 and pi(100)=25,
31509 is in the sequence since 31509=3^4*389 and pi(31509)=3389, and
7560625 is in the sequence since 7560625=5^4*12097 and pi(7560625)=512097.

Mathematica

a251361[n_Integer] := Select[Range[n], PrimePi[#] == FromDigits[
Flatten@ IntegerDigits[First@ Transpose@ FactorInteger[#]]] &]; a251361[10^6] (* Michael De Vlieger, Dec 03 2014 *)

Prog

(PARI) is(n)=eval(fold((x, y)->Str(x, y), factor(n)[, 1]))==primepi(n) \\ Charles R Greathouse IV, Dec 06 2014

Crossrefs

Cf. A000040, A000720, A084317, A251360.

Sequence in context: A324096 A202989 A343183 * A260025 A363815 A218884

Adjacent sequences: A251358 A251359 A251360 * A251362 A251363 A251364

Keyword

nonn,base,more

Author

Jahangeer Kholdi, Dec 02 2014

Status

approved