A257652 The semiprimes which set new records for the sum of their decimal digits.

4, 6, 9, 38, 39, 49, 69, 169, 278, 289, 299, 489, 589, 689, 699, 799, 899, 2899, 3899, 4989, 5899, 5999, 6999, 7999, 9899, 19999, 29999, 48999, 58999, 68999, 69999, 88999, 99899, 299899, 398999, 589989, 589999, 689999, 798999, 889999, 899999, 2899999, 3899999

Offset

1,1

Comments

The semiprimes that set new records in A175013. New records of digit sums of 4, 6, 9, 11, 12, 13, 15, 16, 17,.. are set by the semiprimes 4, 6, 9, 38, 39, 49, 69,...

Links

K. D. Bajpai, Table of n, a(n) for n = 1..64

Example

a(4) = 38 = 2 * 19, which is a semiprime with sum of digits = 3 + 8 = 11.
a(5) = 39 = 3 * 13, which is a semiprime with sum of digits = 3 + 9 = 12. Since 12 > 11, 38 and 39 are in list.

Mathematica

t = {}; s = 0; Do[If[(x = Total[IntegerDigits[n]]) > s && PrimeOmega[n] == 2, AppendTo[t, n]; s = x], {n, 1000000}]; t
DeleteDuplicates[{#, Total[IntegerDigits[#]]}&/@Select[Range[4*10^6], PrimeOmega[#] == 2&], GreaterEqual[ #1[[2]], #2[[2]]]&][[;; , 1]] (* Harvey P. Dale, Apr 12 2024 *)

Crossrefs

Cf. A175013, A068809, A246569.

Subsequence of A213653.

Sequence in context: A303699 A292153 A175459 * A107665 A085733 A242751

Adjacent sequences: A257649 A257650 A257651 * A257653 A257654 A257655

Keyword

nonn,base,changed

Author

K. D. Bajpai, Jul 25 2015

Status

approved