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A338972
Primes p such that the sum of decimal digits of p is the sum of primes dividing p+1 (with repetition).
1
5, 17, 47, 97, 359, 1979, 2399, 5669, 9719, 12799, 79379, 134999, 143999, 161999, 199679, 671999, 679999, 890999, 967999, 974999, 1249999, 3455999, 3583999, 3644999, 4687499, 4976639, 5279999, 5375999, 6298559, 8774999, 16839899, 24959999, 26459999, 29567999, 45359999, 48383999, 68849999
OFFSET
1,1
LINKS
EXAMPLE
a(4) = 97 is in the sequence because 97 is prime, the sum of digits of 97 is 9+7 = 16 and the sum of primes dividing 98=2*7*7 is 2+7+7 = 16.
MAPLE
sod:= n -> convert(convert(n, base, 10), `+`):
spf:= proc(n) local t; add(t[1]*t[2], t=ifactors(n)[2]) end proc:
select(p -> sod(p) = spf(p+1), [seq(ithprime(i), i=1..10^5)]);
PROG
(PARI) isok(p) = if (isprime(p), my(f=factor(p+1)); sumdigits(p) == f[, 1]~*f[, 2]); \\ Michel Marcus, Dec 18 2020
CROSSREFS
Primes in A339805.
Sequence in context: A228857 A253427 A339805 * A332358 A011853 A215053
KEYWORD
nonn,base
AUTHOR
J. M. Bergot and Robert Israel, Dec 18 2020
STATUS
approved