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A129317
The second of the pair of consecutive integers k and k+1 such that sopfr(k) divides sopfr(k+1), where sopfr(k) is the sum of the prime factors of k, counting multiplicity.
5
6, 9, 16, 78, 126, 161, 253, 497, 715, 949, 981, 1046, 1054, 1261, 1331, 1379, 1405, 1431, 1509, 1521, 1611, 1751, 1863, 1891, 2171, 2492, 2681, 2822, 3095, 3101, 3249, 3401, 3592, 3611, 3653, 3809, 4186, 4192, 4385, 4453, 4501, 4599, 4907, 5121, 5146
OFFSET
1,1
COMMENTS
A129316 is the first element of the pair.
A generalization of Ruth-Aaron pairs (A006145).
LINKS
FORMULA
sopfr(k+1) mod sopfr(k) = 0.
a(n) = A129316(n+1). - Amiram Eldar, Oct 26 2019
EXAMPLE
a(6)=161 since sopfr(160)=sopfr(2^5*5)=10+5=15 and sopfr(161)=sopfr(7*23)=30.
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Walter Kehowski, Apr 09 2007
STATUS
approved