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A337845
Primes with a digital sum that is less than the digital sum of the previous prime.
1
11, 23, 31, 41, 53, 61, 71, 83, 97, 101, 113, 131, 151, 163, 173, 181, 211, 233, 241, 263, 271, 281, 307, 311, 331, 353, 367, 373, 383, 397, 401, 421, 443, 457, 461, 487, 491, 503, 521, 563, 571, 593, 601, 613, 631, 653, 661, 683, 691, 701, 727, 733, 743, 751
OFFSET
1,1
LINKS
EXAMPLE
11 has digital sum 2 which is less than the digital sum of the previous prime (7).
MATHEMATICA
s[n_] := Plus @@ IntegerDigits[n]; p = Select[Range[1000], PrimeQ]; p[[1 + Position[Differences[s /@ p], _?(# < 0 &)] // Flatten]] (* Amiram Eldar, Sep 26 2020 *)
Prime[#]&/@(Flatten[Position[Partition[Table[Total[IntegerDigits[Prime[n]]], {n, 200}], 2, 1], _?(#[[2]]<#[[1]]&), 1, Heads->False]]+1) (* Harvey P. Dale, Aug 05 2022 *)
PROG
(PARI) isok(p) = isprime(p) && (sumdigits(p) < sumdigits(precprime(p-1))); \\ Michel Marcus, Sep 26 2020
CROSSREFS
Cf. A007605.
Sequence in context: A060399 A030665 A077501 * A030675 A110786 A059642
KEYWORD
nonn,base
AUTHOR
STATUS
approved